what method did you use to fix your idle
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From: ct
what method did you use to fix your idle
just wanted to now from members with bouncy and high idles ...what you did to get it back to around 750-800 idle ...what was yor step by step procedure
i checked for vaccume leaks, adjusted the t.p.s., intake leak's. anything that has to do with leak.
plus this subject has been beaten to death..try researching the matter. or grab yourself the haynes manuel at your local auto part's store.
plus this subject has been beaten to death..try researching the matter. or grab yourself the haynes manuel at your local auto part's store.
Joined: Dec 2006
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From: Sterling Heights, MI
x infinity
Thread Starter
Rotary Enthusiast
Joined: Feb 2002
Posts: 828
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From: ct
has anyone had any problems with j spec motors...im not asking whether its been covered before its to help new members...decide for themselves what procedure is best for them...this is not a flaming thread its a helping thread ,i resolved mine with a faulty throttle cable
hey i just fixed the idle problem on my 89 gxl my problem was that it would idle between 800 and 1200rpm i couldn't find vacuum leaks, but what i did find made me feel really stupid, i don't know about u guys but i have no clamp on the intake, where the shoulder part of the intake meets the actual intake tube (ur intake should be 2 large hoses one side leads to the filter other leads to the throttle body u should be able to separate the hose into two pieces) anyway the car was warming up and the idle started to surge once again and i just pushed the two tubes together and it stalled i had my brother start the car and keep it going as i pushed the tubes together and it idled perfect didn't surge or anything later i found out there is a sensor in the intake and i pulled it out and cleaned the connections and it idles perfect at 720 doesn't budge and it stopped idling at 5,000 when its cold so it turns out there was a leak in the intake
i figured i would tell everyone who has the same problems that are having no luck
i figured i would tell everyone who has the same problems that are having no luck
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hmmmmmmmmmm........
Thread Starter
Rotary Enthusiast
Joined: Feb 2002
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From: ct
nice job myfirstfc ....when you start to slow down does it hold the idle solid.
also styleemon was your motec plug and play and how much
i found this write up from sript7
RX7 Rough Idle Diagnosis Simplified
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I have read numerous posts from FC and FD owners concerning rough idle or stalling problems and I have a suggestion that should make diagnosing this common problem a bit easier. Please keep in mind that what I am about to suggest is meant to be a quick STARTING POINT for rough idle diagnostics, as there are a number of different causes that can result in a poor idle. I have used this method with great success ever since I started repairing cars for a living in 1976.
First I like to start by trying to determine if the fuel mixture is too rich or too lean. I prefer to use the propane method for this, as it is an alternate fuel source that is controllable, predictable and safer than carb cleaner spray. I use a common propane bottle (torch kit) that I modified using common brass fittings so I can attach a 2 or 3 ft long vacuum hose to it (modifying the torch isn't required, using it as-is will work fine).
If the engine will run at all, have an assistant sit in the car and hold the engine at a constant speed in the 1500-2000 RPM range. (If you don't have an assistant, borrow a neighbor...if you don't have a propane torch, borrow his). Aim the UNLIT torch at the air filter (or intake duct if you are using the stock air box). Slowly open the valve to get the propane flowing into the engine. Pay close attention to how the engine responds. If the RPMs increase and the engine smooths out, your mixture is too lean. If the RPMs drop only slightly, the mixture was most likely in the normal range to begin with. If the RPMs drop considerably with noticeable roughness, a too-rich mixture is suspected. Another way to tell if the mix is too rich is by removing a large vacuum hose (the hose going to the brake booster is a good choice). You can control the size of the vacuum leak with your thumb on the end of the hose. If the engine runs it's smoothest with the air leak that you just created, it was running too rich. This is a generic way to determine fuel mixture. Obviously, a wideband 02 setup or a 5-gas analyzer would be the most accurate, but a good majority of us don't have that luxury.
If you determined that the mixture was too lean, now move your UNLIT torch from the air intake to any point in the engine bay where air might enter the engine, such as cracked vacuum hoses, injector O-rings, torn intake boots, etc. Pay particular attention to the intake manifold flange areas. This is where the vacuum hose adapter on the torch works very well. You can aim the propane exactly where you want it to help pinpoint a leak. It also allows you to keep the propane bottle upright so only gas is expelled and not gas/ liquid. I have found and repaired countless air leaks at the manifold flanges from the use of aftermarket gaskets which most often are made of a thinner material than OEM. Some people slather lots of silicone on both sides of the gaskets to help with this, and although it can work, I don't much care for oozing silicone into the port runners. I don't know of any silicone that doesn't break down from fuel vapors that exist after the engine is shut off.
This propane test is the second best way to find vacuum leaks IMHO. The absolute best way to find them is with a smoke machine that is used at some repair shops. A non-carcinogenic smoke is injected at low pressure throughout the entire intake tract. Wherever there is smoke, there's a vacuum leak. This is yet another luxury that most of us with FCs don't have, but you get the jist.
As with any diagnostic routine, don't rule out other causes of rough idle, such as:
Low/ uneven compression
Fouled spark plugs/ arcing plug wires
Incorrect spark timing
Fuel pressure/ volume/ pump voltage/ regulator internal leaks
Poor grounds/ harness plugs
Loose intake boots/ clamps
--------------------------------------------------------------------------------
also styleemon was your motec plug and play and how much
i found this write up from sript7
RX7 Rough Idle Diagnosis Simplified
--------------------------------------------------------------------------------
I have read numerous posts from FC and FD owners concerning rough idle or stalling problems and I have a suggestion that should make diagnosing this common problem a bit easier. Please keep in mind that what I am about to suggest is meant to be a quick STARTING POINT for rough idle diagnostics, as there are a number of different causes that can result in a poor idle. I have used this method with great success ever since I started repairing cars for a living in 1976.
First I like to start by trying to determine if the fuel mixture is too rich or too lean. I prefer to use the propane method for this, as it is an alternate fuel source that is controllable, predictable and safer than carb cleaner spray. I use a common propane bottle (torch kit) that I modified using common brass fittings so I can attach a 2 or 3 ft long vacuum hose to it (modifying the torch isn't required, using it as-is will work fine).
If the engine will run at all, have an assistant sit in the car and hold the engine at a constant speed in the 1500-2000 RPM range. (If you don't have an assistant, borrow a neighbor...if you don't have a propane torch, borrow his). Aim the UNLIT torch at the air filter (or intake duct if you are using the stock air box). Slowly open the valve to get the propane flowing into the engine. Pay close attention to how the engine responds. If the RPMs increase and the engine smooths out, your mixture is too lean. If the RPMs drop only slightly, the mixture was most likely in the normal range to begin with. If the RPMs drop considerably with noticeable roughness, a too-rich mixture is suspected. Another way to tell if the mix is too rich is by removing a large vacuum hose (the hose going to the brake booster is a good choice). You can control the size of the vacuum leak with your thumb on the end of the hose. If the engine runs it's smoothest with the air leak that you just created, it was running too rich. This is a generic way to determine fuel mixture. Obviously, a wideband 02 setup or a 5-gas analyzer would be the most accurate, but a good majority of us don't have that luxury.
If you determined that the mixture was too lean, now move your UNLIT torch from the air intake to any point in the engine bay where air might enter the engine, such as cracked vacuum hoses, injector O-rings, torn intake boots, etc. Pay particular attention to the intake manifold flange areas. This is where the vacuum hose adapter on the torch works very well. You can aim the propane exactly where you want it to help pinpoint a leak. It also allows you to keep the propane bottle upright so only gas is expelled and not gas/ liquid. I have found and repaired countless air leaks at the manifold flanges from the use of aftermarket gaskets which most often are made of a thinner material than OEM. Some people slather lots of silicone on both sides of the gaskets to help with this, and although it can work, I don't much care for oozing silicone into the port runners. I don't know of any silicone that doesn't break down from fuel vapors that exist after the engine is shut off.
This propane test is the second best way to find vacuum leaks IMHO. The absolute best way to find them is with a smoke machine that is used at some repair shops. A non-carcinogenic smoke is injected at low pressure throughout the entire intake tract. Wherever there is smoke, there's a vacuum leak. This is yet another luxury that most of us with FCs don't have, but you get the jist.
As with any diagnostic routine, don't rule out other causes of rough idle, such as:
Low/ uneven compression
Fouled spark plugs/ arcing plug wires
Incorrect spark timing
Fuel pressure/ volume/ pump voltage/ regulator internal leaks
Poor grounds/ harness plugs
Loose intake boots/ clamps
--------------------------------------------------------------------------------
Thread Starter
Rotary Enthusiast
Joined: Feb 2002
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From: ct
heres another method
IDLE CONTROL SYSTEM
The idle control system is also referred to as the bypass air control (BAC) system. Idle is controlled mainly by the bypass air control (BAC) valve. What is meant by idle control is that the ECU tries to maintain the idle speed that was set as the base idle speed by allowing more bypassed air (in addition to the air already bypassed by the base idle circuit) when needed. There is also an air bypass solenoid valve which plays a role only upon start-up. This below shows the schematics of the idle control system. The BAC valve is the left-most of the two valves.
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BAC VALVE
The BAC valve is part of an air feed line that directs air taken before the throttle plates (in the the air funnel) to the intake manifold after the throttle plates. This air "bypasses" the normal path of air to the intake manifold which is via the throttle bores. The BAC valve is a vibrating valve which opens and closes at a given frequency by being fed a pulse signal by the engine control unit (ECU). The ECU controls how much the BAC valve is actually opened by varying the pulse width. The longer the pulse width, the longer the BAC valve is opened. The ECU controls the BAC valve based upon inputs that affect idle. These inputs are:
crank angle sensor (tells the ECU the engine's speed)
throttle position sensor (tells the ECU the throttle plate angle: a fully closed position puts the ECU in idle mode)
water thermo sensor (tells the ECU the engine coolant temperature)
water temperature switch (tells the ECU the temperature of the air near the radiator)
intake air temperature sensor (tells the ECU the temperature of the air entering the intake)
power steering (P/S) switch (tells the ECU the driver is turning the wheels)
air conditioning (A/C) switch (tells the ECU the A/C compressor is engaged)
neutral switch (tells the ECU the transmission is in neutral)
clutch switch (tells the ECU the clutch pedal is depressed)
inhibitor switch (only an automatic transmission, not discussed here)
initial set switch (for setting idle speed, not discussed here)
The basics behind the BAC valve is that it should allow more air into the engine when the engine load increases. An increase in engine load is sensed by the ECU when the crank angle sensor (CAS) indicates a decrease in engine speed. As an example, when the headlights are turned on, the alternator has to produce more current. It is therefore putting more load on the engine and slowing it down. To prevent the engine from turning too slow (or even stalling), the ECU compensates the increased load by lengthening the pulse width to the BAC valve. This has the effect of increasing the engine speed back to normal idle speed (obtained when there is no load on engine). For some load types, the ECU does not rely on the CAS to detect load increase but on some special switches: P/S, A/C, neutral, and clutch switches.
Please be well aware that the base idle speed does not come from the BAC valve itself, but from some "plumbing" within the intake. The base idle speed (750 rpm) can be adjusted by turning the capped screw on top of the intake. It has nothing to do with the BAC valve, and this is why you should always adjust the base idle speed by setting the initial set coupler or disconnecting the BAC connector (at the BAC valve).
The BAC valve connects to the main relay through a B/W (black with white stripe) wire and to pin 2Q of the ECU through a L/G (blue with green stripe) wire. The main relay has a 12V DC voltage when the engine is running. Pin 2Q is a pulse (square) signal at a fixed frequency provided by the ECU. The BAC valve is closed when the voltage at pin 2Q is 12V and open when the voltage is 0V (grounded). This means that the longer the valve stays open, the lower the DC voltage at pin 2Q is. The DC voltage that is measured at pin 2Q is the average of the actual pulse voltage. To sum it up, the lower the DC voltage at pin 2Q is, the longer the pulse width (0V pulse) is and the longer the valve stays open (the more air passes through the BAC valve). As an example, the DC voltage at pin 2Q will drop if the headlights are turned on (maybe from 11.5V to 11V). If the defroster is also turned on, it will drop even further (maybe, from 11V to 10.5V).
AIR BYPASS SOLENOID VALVE
This valve bypasses air to the intake when a "cold" engine is started up. It is a solenoid valve, meaning it is open when energized (it is not a vibrating valve like the BAC valve).
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This above is the factory service manual (FSM) check for proper operation of the air bypass solenoid valve and the circuit diagram for the valve and its relay. The air bypass solenoid valve is open when 12V is applied between its terminals. One of the two terminal connects to the main relay via a B/W (black with white stripe) wire. The other terminal connects to the air bypass relay via a Br/Y (brown with yellow stripe) wire. Since the B/W wire sees 12V when engine running, the Br/Y wire must be at 0V (grounded) to energize and therefore open the valve. When a cold engine is started, the air bypass solenoid valve is energized for 17 seconds to allow for extra bypassed air. This is an accelerated warmup system. The air bypass relay is here to ground the Br/Y wire when the ECU energizes its coil side (0V at pin 1C).
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Copyright © 2003 - The MAZDA RX-7 86-88 Technical Page - All Rights Reserved
The idle control system is also referred to as the bypass air control (BAC) system. Idle is controlled mainly by the bypass air control (BAC) valve. What is meant by idle control is that the ECU tries to maintain the idle speed that was set as the base idle speed by allowing more bypassed air (in addition to the air already bypassed by the base idle circuit) when needed. There is also an air bypass solenoid valve which plays a role only upon start-up. This below shows the schematics of the idle control system. The BAC valve is the left-most of the two valves.
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BAC VALVE
The BAC valve is part of an air feed line that directs air taken before the throttle plates (in the the air funnel) to the intake manifold after the throttle plates. This air "bypasses" the normal path of air to the intake manifold which is via the throttle bores. The BAC valve is a vibrating valve which opens and closes at a given frequency by being fed a pulse signal by the engine control unit (ECU). The ECU controls how much the BAC valve is actually opened by varying the pulse width. The longer the pulse width, the longer the BAC valve is opened. The ECU controls the BAC valve based upon inputs that affect idle. These inputs are:
crank angle sensor (tells the ECU the engine's speed)
throttle position sensor (tells the ECU the throttle plate angle: a fully closed position puts the ECU in idle mode)
water thermo sensor (tells the ECU the engine coolant temperature)
water temperature switch (tells the ECU the temperature of the air near the radiator)
intake air temperature sensor (tells the ECU the temperature of the air entering the intake)
power steering (P/S) switch (tells the ECU the driver is turning the wheels)
air conditioning (A/C) switch (tells the ECU the A/C compressor is engaged)
neutral switch (tells the ECU the transmission is in neutral)
clutch switch (tells the ECU the clutch pedal is depressed)
inhibitor switch (only an automatic transmission, not discussed here)
initial set switch (for setting idle speed, not discussed here)
The basics behind the BAC valve is that it should allow more air into the engine when the engine load increases. An increase in engine load is sensed by the ECU when the crank angle sensor (CAS) indicates a decrease in engine speed. As an example, when the headlights are turned on, the alternator has to produce more current. It is therefore putting more load on the engine and slowing it down. To prevent the engine from turning too slow (or even stalling), the ECU compensates the increased load by lengthening the pulse width to the BAC valve. This has the effect of increasing the engine speed back to normal idle speed (obtained when there is no load on engine). For some load types, the ECU does not rely on the CAS to detect load increase but on some special switches: P/S, A/C, neutral, and clutch switches.
Please be well aware that the base idle speed does not come from the BAC valve itself, but from some "plumbing" within the intake. The base idle speed (750 rpm) can be adjusted by turning the capped screw on top of the intake. It has nothing to do with the BAC valve, and this is why you should always adjust the base idle speed by setting the initial set coupler or disconnecting the BAC connector (at the BAC valve).
The BAC valve connects to the main relay through a B/W (black with white stripe) wire and to pin 2Q of the ECU through a L/G (blue with green stripe) wire. The main relay has a 12V DC voltage when the engine is running. Pin 2Q is a pulse (square) signal at a fixed frequency provided by the ECU. The BAC valve is closed when the voltage at pin 2Q is 12V and open when the voltage is 0V (grounded). This means that the longer the valve stays open, the lower the DC voltage at pin 2Q is. The DC voltage that is measured at pin 2Q is the average of the actual pulse voltage. To sum it up, the lower the DC voltage at pin 2Q is, the longer the pulse width (0V pulse) is and the longer the valve stays open (the more air passes through the BAC valve). As an example, the DC voltage at pin 2Q will drop if the headlights are turned on (maybe from 11.5V to 11V). If the defroster is also turned on, it will drop even further (maybe, from 11V to 10.5V).
AIR BYPASS SOLENOID VALVE
This valve bypasses air to the intake when a "cold" engine is started up. It is a solenoid valve, meaning it is open when energized (it is not a vibrating valve like the BAC valve).
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This above is the factory service manual (FSM) check for proper operation of the air bypass solenoid valve and the circuit diagram for the valve and its relay. The air bypass solenoid valve is open when 12V is applied between its terminals. One of the two terminal connects to the main relay via a B/W (black with white stripe) wire. The other terminal connects to the air bypass relay via a Br/Y (brown with yellow stripe) wire. Since the B/W wire sees 12V when engine running, the Br/Y wire must be at 0V (grounded) to energize and therefore open the valve. When a cold engine is started, the air bypass solenoid valve is energized for 17 seconds to allow for extra bypassed air. This is an accelerated warmup system. The air bypass relay is here to ground the Br/Y wire when the ECU energizes its coil side (0V at pin 1C).
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Copyright © 2003 - The MAZDA RX-7 86-88 Technical Page - All Rights Reserved
Thread Starter
Rotary Enthusiast
Joined: Feb 2002
Posts: 828
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From: ct
paul stoaks method
Diagnosing Turbo II Idle Problems
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There are a variety of possible failure modes in the idle circuit. This writeup describes trouble-shooting to identify the most common causes of problems. The first five items thoroughtly check the idle control loop, centered on the BAC control circuit. The shop manual adequately describes how to check the other components and sensors. The next few items give a couple of other things that can be checked and, finally, help is offered in case the ECU is found to be defective.
Symptoms:
Car idles at about 600 RPM.
Idle can not be increased with idle speed screw.
Car frequently dies when AC is on.
Disconnecting BAC valve connector (as per shop manual) does not change idle.
Extreme hot starting problems.
Check the following, in order:
1. Check to see if a jumper has been left in the initial set connector. It's easy to forget to remove this after adjusting idle speed. On '87-'88 models, the initial set connector is a green connector with two female spade connectors in it, placed at right angles to each other. It is located in the engine compartment, forward on the driver's side, near the headlight. On later models, it is a single conductor connector, located in about the same position. In these models, a jumper is connected between the connector and ground.
2. Check the Throttle Position Sensor setting. A variety of instructions for doing this are contained in the FAQ. My personal favorite is the two light bulbs. After setting it, rev the engine a couple of times to let everything settle back into place, and re-check it. You may even want to take the car for a quick drive and re-check the setting. An incorrectly set TPS seems to be the most frequent idle culprit. Make sure you get it right.
If you are still having problems, you probably have some kind of component failure. The tests now get a little more sophisticated.
3. Turn off the ignition. Remove the connector from the BAC valve and check the resistance of the BAC valve solenoid. This is done by connecting an ohm-meter across the BAC valve terminals. Care must be taken not to let the probes touch each other or you will get a false reading. You should get somewhere between 10 and 20 ohms. The manual says 10.7 to 12.3 ohms, but it's really not that picky. What you don't want is near zero ohms (solenoid is shorted) or very high resistance (solenoid is open-circuit.) If you have a shorted or open-circuit solenoid, you will need to replace the BAC valve. You might want to try disassembling it just on the off chance that it is repairable.
4. With the connector still removed, and the engine still off, place a 10k ohm, 1/4 watt resistor across the terminals of the connector. This is easy to do, simply insert the resistor leads into the connector. Make sure that the leads of the resistor do not short against each other or anything else. Turn the ignition on, without starting the car, and measure the AC voltage across the resistor. You should get a value between 6 and 7 volts after it settles down. A voltage lower than 5V indicates a likely ECU failure. Go here for more information. If you get the correct voltage, move on to the next step.
NOTE: This is a good chance to check that the conductors in the connector are firmly seated. Mine came loose, slid down, and shorted out, causing ECU failure. More on that in a moment. At the very least, if they are sliding around, they aren't making good contact. If you find that the conductors are loose in the connector, press the wires from the back of the connector towards the front. They should snap into place and not slide back. If they do slide back, you will need to either get a new connector, or epoxy them in, like I did. It works. (Be careful not to get epoxy on the connector surfaces!)
NOTE: Do not perform the following test if you obtained a reading of 0 ohms (short circuit) when you measured the resistance of the solenoid above. Something will get *very* hot.
5. The BAC valve may be stuck. Using jumper wires, connect 12V across the solenoid leads, being extremely careful not to create a short. If you didn't get an open-circuit reading when you measured the resistance of the BAC valve, the valve should click. If it is stuck, doing this a couple of times should free up the valve. I would also recommend removing the BAC valve from the intake manifold (this can be accomplished without removing the water hoses connected to the valve) and spraying WD-40 into it. Work it a few more times with 12V. If you can't get the thing to click this way, replace the BAC valve.
If you got to this point and you are still having idle problems, the problem is not in the electronic idle control system. Here are a few other possibilities and a few ways to check them:
1. Vacuum Leak
Vacuum leaks are frequently the cause of rough idle. A leak ruins your idle by allowing un-metered air to enter the intake manifold, creating a lean air-fuel mixture. Leaks typically develop as a result of vacuum or pressure hoses coming loose or failing, or gasket failures.
Vacuum leaks are frequently diagnosed and located by spraying some kind of flammable substance around the engine. When the flammable substance is sucked in through the leak, the lean condition is temporarily rectified and the engine will speed up. As can be imagined, spraying flammable substances around hot, running engines is a potentially very dangerous practice. It may best be left to qualified service personnel. "Poof, no eybrows!!" I don't even want to suggest flammable substances that can be used here.
A safer method that I have sometimes used successfully is to use a mechanic's stethoscope or a piece of vacuum tubing stuck in your ear. Use the other end to probe around the engine, listening for a hissing or whistling noise. I have successfully found both vacuum and exhaust leaks using this method.
2. Leaks in Intake Hoses
Leaks in the intake hoses after the Mass Airflow Sensor can result in bad idle in exactly the same manner as the vacuum leak. Again, the problem is unmetered air entering the engine. The best way to find these is simply by inspecting all of the components between the MAF and the throttle body.
On a TII, the problem is frequently the hose that connects the MAF to the turbo inlet. This hose has a tendancy to split, which lets air pass. A very small split can cause pretty big problems. Splits can sometimes be fixed with some RTV, but you need to be careful not to let the stuff get into the turbo. Also, make sure you use sealant that is O2 sensor safe. If you can afford it, or have access to a good used, hose, replace it.
3. Obstructed Exhaust System
At least one Rx7 list contributor has had problems with his idle as a result of plugged catalytic converters. I don't know how to check for this. If you do, let us know, and we'll put it here.
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ECU Problems?
If you discovered that your ECU was not sending the correct signal from step 4, please contact me (via direct E-mail, pstoaks@savantage.com.) There is a fix and a work-around which I am writing up, but I would like to get a sense for how many people have experienced this failure. Rest assured, the fix costs a little time and less than $1.00. The workarounds take a little less time and still cost less than $10.00.
For those of you who are handy with electronics, the ECU fix is to replace the BAC valve output transistor. On my ECU (which is an N332), the transistor is T801, which is the last power transistor in line to the left of center of the ECU (on the bottom board.) If you have a different ECU, you can find the correct transistor by tracing the circuit with an ohm-meter, starting with connector pin 2Q (see the diagram in the shop manual). This pin is connected directly to the collector of the output transistor. (If you do this, please send me the info so I can get it in here for everyone else.) My transistor was an NEC D1309, which I couldn't cross reference. Since it is only wired as an open collector switch, though, close is good enough. I used a readily available TIP120 (NPN Darlington) and it worked great. Just desolder the old one and solder in the new one, and you're in business. The failure? Severe degredation of Hfe from heat. In my case, this was caused by the shorting of the BAC valve connector conductors. Another TeamFC3S member contracted what we believe to be this same problem after letting a service shop do a regularly scheduled tune-up! On two different cars! This suggests a potential problem in the diagnostic procedures used.
Yet another TeamFC3S member had a burned out resistor in the output section. I don't yet know which resistor it was. I have traced out the circuit and can't figure it out. However, replacing the resistor cured his problem.
For the rest of you, I am going to write up a detailed repair procedure that you can follow, complete with pictures. It could take me a little while, so please be patient. I am also working on a write-up of the bolt-on fix mentioned above.
I am also very interested in hearing from those who have had these symptoms and took the car to the shop. What was the result? How much did a cure cost, and what were you told was the problem?
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There are a variety of possible failure modes in the idle circuit. This writeup describes trouble-shooting to identify the most common causes of problems. The first five items thoroughtly check the idle control loop, centered on the BAC control circuit. The shop manual adequately describes how to check the other components and sensors. The next few items give a couple of other things that can be checked and, finally, help is offered in case the ECU is found to be defective.
Symptoms:
Car idles at about 600 RPM.
Idle can not be increased with idle speed screw.
Car frequently dies when AC is on.
Disconnecting BAC valve connector (as per shop manual) does not change idle.
Extreme hot starting problems.
Check the following, in order:
1. Check to see if a jumper has been left in the initial set connector. It's easy to forget to remove this after adjusting idle speed. On '87-'88 models, the initial set connector is a green connector with two female spade connectors in it, placed at right angles to each other. It is located in the engine compartment, forward on the driver's side, near the headlight. On later models, it is a single conductor connector, located in about the same position. In these models, a jumper is connected between the connector and ground.
2. Check the Throttle Position Sensor setting. A variety of instructions for doing this are contained in the FAQ. My personal favorite is the two light bulbs. After setting it, rev the engine a couple of times to let everything settle back into place, and re-check it. You may even want to take the car for a quick drive and re-check the setting. An incorrectly set TPS seems to be the most frequent idle culprit. Make sure you get it right.
If you are still having problems, you probably have some kind of component failure. The tests now get a little more sophisticated.
3. Turn off the ignition. Remove the connector from the BAC valve and check the resistance of the BAC valve solenoid. This is done by connecting an ohm-meter across the BAC valve terminals. Care must be taken not to let the probes touch each other or you will get a false reading. You should get somewhere between 10 and 20 ohms. The manual says 10.7 to 12.3 ohms, but it's really not that picky. What you don't want is near zero ohms (solenoid is shorted) or very high resistance (solenoid is open-circuit.) If you have a shorted or open-circuit solenoid, you will need to replace the BAC valve. You might want to try disassembling it just on the off chance that it is repairable.
4. With the connector still removed, and the engine still off, place a 10k ohm, 1/4 watt resistor across the terminals of the connector. This is easy to do, simply insert the resistor leads into the connector. Make sure that the leads of the resistor do not short against each other or anything else. Turn the ignition on, without starting the car, and measure the AC voltage across the resistor. You should get a value between 6 and 7 volts after it settles down. A voltage lower than 5V indicates a likely ECU failure. Go here for more information. If you get the correct voltage, move on to the next step.
NOTE: This is a good chance to check that the conductors in the connector are firmly seated. Mine came loose, slid down, and shorted out, causing ECU failure. More on that in a moment. At the very least, if they are sliding around, they aren't making good contact. If you find that the conductors are loose in the connector, press the wires from the back of the connector towards the front. They should snap into place and not slide back. If they do slide back, you will need to either get a new connector, or epoxy them in, like I did. It works. (Be careful not to get epoxy on the connector surfaces!)
NOTE: Do not perform the following test if you obtained a reading of 0 ohms (short circuit) when you measured the resistance of the solenoid above. Something will get *very* hot.
5. The BAC valve may be stuck. Using jumper wires, connect 12V across the solenoid leads, being extremely careful not to create a short. If you didn't get an open-circuit reading when you measured the resistance of the BAC valve, the valve should click. If it is stuck, doing this a couple of times should free up the valve. I would also recommend removing the BAC valve from the intake manifold (this can be accomplished without removing the water hoses connected to the valve) and spraying WD-40 into it. Work it a few more times with 12V. If you can't get the thing to click this way, replace the BAC valve.
If you got to this point and you are still having idle problems, the problem is not in the electronic idle control system. Here are a few other possibilities and a few ways to check them:
1. Vacuum Leak
Vacuum leaks are frequently the cause of rough idle. A leak ruins your idle by allowing un-metered air to enter the intake manifold, creating a lean air-fuel mixture. Leaks typically develop as a result of vacuum or pressure hoses coming loose or failing, or gasket failures.
Vacuum leaks are frequently diagnosed and located by spraying some kind of flammable substance around the engine. When the flammable substance is sucked in through the leak, the lean condition is temporarily rectified and the engine will speed up. As can be imagined, spraying flammable substances around hot, running engines is a potentially very dangerous practice. It may best be left to qualified service personnel. "Poof, no eybrows!!" I don't even want to suggest flammable substances that can be used here.
A safer method that I have sometimes used successfully is to use a mechanic's stethoscope or a piece of vacuum tubing stuck in your ear. Use the other end to probe around the engine, listening for a hissing or whistling noise. I have successfully found both vacuum and exhaust leaks using this method.
2. Leaks in Intake Hoses
Leaks in the intake hoses after the Mass Airflow Sensor can result in bad idle in exactly the same manner as the vacuum leak. Again, the problem is unmetered air entering the engine. The best way to find these is simply by inspecting all of the components between the MAF and the throttle body.
On a TII, the problem is frequently the hose that connects the MAF to the turbo inlet. This hose has a tendancy to split, which lets air pass. A very small split can cause pretty big problems. Splits can sometimes be fixed with some RTV, but you need to be careful not to let the stuff get into the turbo. Also, make sure you use sealant that is O2 sensor safe. If you can afford it, or have access to a good used, hose, replace it.
3. Obstructed Exhaust System
At least one Rx7 list contributor has had problems with his idle as a result of plugged catalytic converters. I don't know how to check for this. If you do, let us know, and we'll put it here.
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ECU Problems?
If you discovered that your ECU was not sending the correct signal from step 4, please contact me (via direct E-mail, pstoaks@savantage.com.) There is a fix and a work-around which I am writing up, but I would like to get a sense for how many people have experienced this failure. Rest assured, the fix costs a little time and less than $1.00. The workarounds take a little less time and still cost less than $10.00.
For those of you who are handy with electronics, the ECU fix is to replace the BAC valve output transistor. On my ECU (which is an N332), the transistor is T801, which is the last power transistor in line to the left of center of the ECU (on the bottom board.) If you have a different ECU, you can find the correct transistor by tracing the circuit with an ohm-meter, starting with connector pin 2Q (see the diagram in the shop manual). This pin is connected directly to the collector of the output transistor. (If you do this, please send me the info so I can get it in here for everyone else.) My transistor was an NEC D1309, which I couldn't cross reference. Since it is only wired as an open collector switch, though, close is good enough. I used a readily available TIP120 (NPN Darlington) and it worked great. Just desolder the old one and solder in the new one, and you're in business. The failure? Severe degredation of Hfe from heat. In my case, this was caused by the shorting of the BAC valve connector conductors. Another TeamFC3S member contracted what we believe to be this same problem after letting a service shop do a regularly scheduled tune-up! On two different cars! This suggests a potential problem in the diagnostic procedures used.
Yet another TeamFC3S member had a burned out resistor in the output section. I don't yet know which resistor it was. I have traced out the circuit and can't figure it out. However, replacing the resistor cured his problem.
For the rest of you, I am going to write up a detailed repair procedure that you can follow, complete with pictures. It could take me a little while, so please be patient. I am also working on a write-up of the bolt-on fix mentioned above.
I am also very interested in hearing from those who have had these symptoms and took the car to the shop. What was the result? How much did a cure cost, and what were you told was the problem?
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HalifaxFD
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