Idle problem conquered!
08-28-01, 04:14 PM
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Idle problem conquered!
I finally fixed my hot idle problem after two years!
1990 RX-7 NA vert.
The symptoms: The car would stall at idle every time I came to a light with the AC on and blower on. This would only happen on a very hot day, other times it would be perfectly fine. Turning the AC on would always decrease the idle instead of increasing it. I’ve had this problem for two years and it’s been driving me mad.
Here’s what I did in the order I did it…..
1. Checked TPS and timing a zillion times over 2 years and it was always OK. Idle was crap. Car would stall as noted above.
2. Installed a new 100 amp alternator from a 3rd gen RX-7. Still had the idle problem. See post here… https://www.rx7club.com/vforums/show...&threadid=6349
3. I removed my BAC and tested operation with 12vdc applied---it was OK
4. I tested the BAC resistance---OK at 20 ohms
5. I put a 10K ohm resistor across the BAC connector and measured the AC voltage with my DVM. According to previous posts it is supposed to be between 6 to 7 volts AC. If it is less than 5VAC, apparently the ECU circuit is bad. Mine measures 6.4 to 6.5 VAC, so this looked OK. Still the idle was crap.
6. Last week while setting the TPS with the two light bulb technique I burned two resistors in the ECU. 12vdc appeared on all three pins of the test connector and my engine light came on indicating a switch solenoid fault and relief solenoid fault and a feedback sensor fault. The guy that repaired the two resistors in the ECU http://www.autoecu.com said he does not recommend this technique and thought the bulbs pulled too much current and burned the resistors. I specifically asked him to look at my BAC circuit while it was there and he said the board was functioning fine. I’ll use the DVM technique next time to set my TPS.
7. The burned resistors were not related to my original hot idle problem, but caused me to get into the ECU area and look around. I noticed all the solder joints in the ECU were in excellent condition (except for the two toasted resistors). There was a little corrosion in the lower right hand corner of the board near connector 1A and on one of the connector pins near 1A.
8. When I got the board back from the ECU guy I sprayed the boards and all the connectors (and mating connectors) with CRC 2-26 electrical grade cleaner http://www.crcindustries.com/. THE ECU IS NOT IN THE CAR AT THIS POINT---NO POWER APPLIED. CRC-26 apparently improves electrical properties and gets rid of corrosion. You can probably buy it at http://www.newark.com. I let it sit overnight (ECU opened) to dry. It left an oily film, but the corrosion was completely gone. DO NOT APPLY POWER TO YOUR ECU BEFORE IT IS DRY. I also sprayed CRC on the BAC connectors and TPS connectors.
9. I called tech support at CRC Industries and they said the oily film was non-conductive, but they were worried it would attract dust. I decided to clean the boards with Radio Shack “Electronic Cleaner” # 64-4327 to get rid of the oily film. I let this dry in the sun for several hours until I was sure it was dry. I left the oily film on all the connectors to add a little corrosion protection.
10. I decided to add a test connector to 21 of my ECU wires so I could measure all the sensors with the ECU back in place. This allows me to monitor signals like the thermosensors, BAC, VDI and 6PI with a DVM on my front seat. I’ve found it very useful. See my post here…. https://www.rx7club.com/vforums/show...threadid=17731
11. I also decided to follow the advice of another RX enthusiast and added two 10ga ground wires to pins 3A, 3B, 3C and 3D. Prior to grounding these, I measured 0.2 vdc on one pair of these. See his description here…. http://home.earthlink.net/~burntoast/3700.html
12. I also cut into my TPS wires (harness side in engine compartment) and installed a two prong female molex connector on pins 2F and 2G so I can easily measure the TPS voltages with my DVM. I tie wrapped the connector so it’s not flopping around. Make sure the pins don’t push the out the front and short to ground---I siliconed them on the back side to keep them in place.
13. With everything back in place and the car running, I adjusted my TPS using a DVM and my idle is now perfect. It’s really hot today and under these conditions the car would generally stall at every light with the AC on. I took it for a spin and to my amazement the idle was perfect. With the AC on and blower on high, the idle now increases instead of stalling the car. It will bounce lower for a second as I push the clutch in and come to a stop, but moves up by itself to about 750RPM and settles in just fine.
Hmmm…which one was it?
ECU Pin measurements from new test connector.
Test Condition: Car is hot. According to a meat thermometer in contact with the engine near the engine thermosensor it’s 165 F. I just got back from a long run in 90 degree weather. Idle is perfect.
1. ECU pin 2L, Engine Thermosensor (input). According to the manual it is supposed to be 1 to 2 volts at 176 degrees F at idle. I’m measuring 2.5 to 3.6 vdc, so I’ll probably replace this sensor.
2. Airflow meter (Vs) pin 2B (input) measured 2.8 to 3.8 vdc at idle. Spec is 2.5 to 3.5 vdc (pretty close). Key on, car off measured 4.0 to 5.6vdc and jumping around. It’s supposed to be 4.0 vdc. Not sure of impact.
3. Pin 2I Sensors (output) measured 5.5 to 7.3 vdc key on, car off. Supposed to be 4.5 to 5.5 vdc. Not sure of impact, but this voltage is generated inside ECU and is probably why 2B is high.
4. Pin 2E water thermosensor (input) measured 0.4 to 0.5 vdc at idle engine hot. Spec is 0.3 to 1.0 vdc, so this is OK.
5. Pin 2K Intake Air Thermosensor (input from airflow meter). The spec is 2 to 3 vdc at idle at 68 F. I guess I’ll need to wait till winter to measure this one. I’m seeing 1.1 vdc at 165 F.
6. Pin 3Q BAC (output). I’m measuring 7.0 vdc with the key on. It’s supposed to be approx 9 vdc. At idle I measure 9.4vdc and the spec is approx. 9vdc, so it’s probably OK. I may put an oscilloscope on this lead for shts and grins to see the duty signal pulse with AC on and AC off. If I do, I’ll post the pic. This would be the most conclusive measurement. I’m not too concerned right now because my idle problem is fixed.
Hope this helps guys!
My happy ride....
1990 RX-7 NA vert.
The symptoms: The car would stall at idle every time I came to a light with the AC on and blower on. This would only happen on a very hot day, other times it would be perfectly fine. Turning the AC on would always decrease the idle instead of increasing it. I’ve had this problem for two years and it’s been driving me mad.
Here’s what I did in the order I did it…..
1. Checked TPS and timing a zillion times over 2 years and it was always OK. Idle was crap. Car would stall as noted above.
2. Installed a new 100 amp alternator from a 3rd gen RX-7. Still had the idle problem. See post here… https://www.rx7club.com/vforums/show...&threadid=6349
3. I removed my BAC and tested operation with 12vdc applied---it was OK
4. I tested the BAC resistance---OK at 20 ohms
5. I put a 10K ohm resistor across the BAC connector and measured the AC voltage with my DVM. According to previous posts it is supposed to be between 6 to 7 volts AC. If it is less than 5VAC, apparently the ECU circuit is bad. Mine measures 6.4 to 6.5 VAC, so this looked OK. Still the idle was crap.
6. Last week while setting the TPS with the two light bulb technique I burned two resistors in the ECU. 12vdc appeared on all three pins of the test connector and my engine light came on indicating a switch solenoid fault and relief solenoid fault and a feedback sensor fault. The guy that repaired the two resistors in the ECU http://www.autoecu.com said he does not recommend this technique and thought the bulbs pulled too much current and burned the resistors. I specifically asked him to look at my BAC circuit while it was there and he said the board was functioning fine. I’ll use the DVM technique next time to set my TPS.
7. The burned resistors were not related to my original hot idle problem, but caused me to get into the ECU area and look around. I noticed all the solder joints in the ECU were in excellent condition (except for the two toasted resistors). There was a little corrosion in the lower right hand corner of the board near connector 1A and on one of the connector pins near 1A.
8. When I got the board back from the ECU guy I sprayed the boards and all the connectors (and mating connectors) with CRC 2-26 electrical grade cleaner http://www.crcindustries.com/. THE ECU IS NOT IN THE CAR AT THIS POINT---NO POWER APPLIED. CRC-26 apparently improves electrical properties and gets rid of corrosion. You can probably buy it at http://www.newark.com. I let it sit overnight (ECU opened) to dry. It left an oily film, but the corrosion was completely gone. DO NOT APPLY POWER TO YOUR ECU BEFORE IT IS DRY. I also sprayed CRC on the BAC connectors and TPS connectors.
9. I called tech support at CRC Industries and they said the oily film was non-conductive, but they were worried it would attract dust. I decided to clean the boards with Radio Shack “Electronic Cleaner” # 64-4327 to get rid of the oily film. I let this dry in the sun for several hours until I was sure it was dry. I left the oily film on all the connectors to add a little corrosion protection.
10. I decided to add a test connector to 21 of my ECU wires so I could measure all the sensors with the ECU back in place. This allows me to monitor signals like the thermosensors, BAC, VDI and 6PI with a DVM on my front seat. I’ve found it very useful. See my post here…. https://www.rx7club.com/vforums/show...threadid=17731
11. I also decided to follow the advice of another RX enthusiast and added two 10ga ground wires to pins 3A, 3B, 3C and 3D. Prior to grounding these, I measured 0.2 vdc on one pair of these. See his description here…. http://home.earthlink.net/~burntoast/3700.html
12. I also cut into my TPS wires (harness side in engine compartment) and installed a two prong female molex connector on pins 2F and 2G so I can easily measure the TPS voltages with my DVM. I tie wrapped the connector so it’s not flopping around. Make sure the pins don’t push the out the front and short to ground---I siliconed them on the back side to keep them in place.
13. With everything back in place and the car running, I adjusted my TPS using a DVM and my idle is now perfect. It’s really hot today and under these conditions the car would generally stall at every light with the AC on. I took it for a spin and to my amazement the idle was perfect. With the AC on and blower on high, the idle now increases instead of stalling the car. It will bounce lower for a second as I push the clutch in and come to a stop, but moves up by itself to about 750RPM and settles in just fine.
Hmmm…which one was it?
ECU Pin measurements from new test connector.
Test Condition: Car is hot. According to a meat thermometer in contact with the engine near the engine thermosensor it’s 165 F. I just got back from a long run in 90 degree weather. Idle is perfect.
1. ECU pin 2L, Engine Thermosensor (input). According to the manual it is supposed to be 1 to 2 volts at 176 degrees F at idle. I’m measuring 2.5 to 3.6 vdc, so I’ll probably replace this sensor.
2. Airflow meter (Vs) pin 2B (input) measured 2.8 to 3.8 vdc at idle. Spec is 2.5 to 3.5 vdc (pretty close). Key on, car off measured 4.0 to 5.6vdc and jumping around. It’s supposed to be 4.0 vdc. Not sure of impact.
3. Pin 2I Sensors (output) measured 5.5 to 7.3 vdc key on, car off. Supposed to be 4.5 to 5.5 vdc. Not sure of impact, but this voltage is generated inside ECU and is probably why 2B is high.
4. Pin 2E water thermosensor (input) measured 0.4 to 0.5 vdc at idle engine hot. Spec is 0.3 to 1.0 vdc, so this is OK.
5. Pin 2K Intake Air Thermosensor (input from airflow meter). The spec is 2 to 3 vdc at idle at 68 F. I guess I’ll need to wait till winter to measure this one. I’m seeing 1.1 vdc at 165 F.
6. Pin 3Q BAC (output). I’m measuring 7.0 vdc with the key on. It’s supposed to be approx 9 vdc. At idle I measure 9.4vdc and the spec is approx. 9vdc, so it’s probably OK. I may put an oscilloscope on this lead for shts and grins to see the duty signal pulse with AC on and AC off. If I do, I’ll post the pic. This would be the most conclusive measurement. I’m not too concerned right now because my idle problem is fixed.
Hope this helps guys!
My happy ride....
08-28-01, 08:04 PM
#3
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Here are a few more ECU measurements from my test connector:
Pin 2M, solenoid valve VDI: Spec is approx 12 vdc < 5200 RPM and below 2 vdc above 5200 rpm. I put my dvm on the front seat and can feel it big time in the seat of the pants when it switches near 5500 rpm.
Pin 3R, 6 port induction 6PI: spec is < 2vdc above 3850 rpm and approx 12 vdc < 3850 rpm. My car switches between 4000 and 4500 rpm. I can't really feel anything so I'll look at the actuator rods to make sure they are opening. They do move freely. I still have the air pump.
DISCLAIMER
PROCEED AT YOUR OWN RISK WHEN CLEANING THE ECU. FOLLOW THE MANUFACTURERS INSTRUCTIONS AND MAKE SURE IT IS DRY BEFORE APPLYING POWER!
VERIFY PIN OUTS FOR YOUR YEAR VEHICLE BEFORE GROUNDING ANYTHING. THE PIN OUTS ARE DIFFERENT BETWEEN MODELS. REFER TO YOUR FACTORY MANUAL.
Pin 2M, solenoid valve VDI: Spec is approx 12 vdc < 5200 RPM and below 2 vdc above 5200 rpm. I put my dvm on the front seat and can feel it big time in the seat of the pants when it switches near 5500 rpm.
Pin 3R, 6 port induction 6PI: spec is < 2vdc above 3850 rpm and approx 12 vdc < 3850 rpm. My car switches between 4000 and 4500 rpm. I can't really feel anything so I'll look at the actuator rods to make sure they are opening. They do move freely. I still have the air pump.
DISCLAIMER
PROCEED AT YOUR OWN RISK WHEN CLEANING THE ECU. FOLLOW THE MANUFACTURERS INSTRUCTIONS AND MAKE SURE IT IS DRY BEFORE APPLYING POWER!
VERIFY PIN OUTS FOR YOUR YEAR VEHICLE BEFORE GROUNDING ANYTHING. THE PIN OUTS ARE DIFFERENT BETWEEN MODELS. REFER TO YOUR FACTORY MANUAL.
Last edited by RXster; 08-28-01 at 08:07 PM.
08-29-01, 08:03 AM
#4
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RXster I have been fighting a similar idle problem except my vert idles great with the air on but not with it off. I idled it up so it doesn't stall at lights - it drops to 500rpm the bouces back to 600-700 depending on its mood. I do have the switching soleniod error code. Timing, tps and the bac all are set or test perfectly.
Hope you help me here - when you set your idle which inital set connector are you using? I have both a blue six wire and sigle wire connector and a green set which one do you use to set your idle?
Im going to have to find a local shop that can check out my ECU - (Im about 5000 miles away from Florida) Im not confident enough to jump in to my own ECU - what did autoecu charge? I hope its less than a new BAC because that is the only thing I haven't yet tried.
Hope you help me here - when you set your idle which inital set connector are you using? I have both a blue six wire and sigle wire connector and a green set which one do you use to set your idle?
Im going to have to find a local shop that can check out my ECU - (Im about 5000 miles away from Florida) Im not confident enough to jump in to my own ECU - what did autoecu charge? I hope its less than a new BAC because that is the only thing I haven't yet tried.
08-29-01, 12:07 PM
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This is according to the 90 manual...check to make sure your pin out is the same:
Pin 2O of the ECU is the switch solenoid output. With the key on there should be 12 vdc with your TPS in the idle position. When you move the TPS to half throttle it should drop to less than 2.0 vdc. Try to slide a dental probe or something in the back side of the ECU connector to make this measurement. Don't short it to ground!
When my resistor fried (both the 2O leg and 2P leg inside the ECU) I had 12 vdc on all three check connector pins (the one for setting the TPS). It's really easy to find inside the ECU. Find the 2O pin and follow the trace. The very first resistor is the one that burnt. The guy I mentioned in the post is VERY reasonable and accepts ECU's via UPS with a 1 day turnaround. Call his 800 # first and ask for Don.
I'm not sure what you mean when you say adjust your idle and talk about connectors. On my 90 vert there is a single pin connector front drivers side near the battery. This must be grounded before setting your idle (accessories off). With your switch error you can't use the lightbulb technique to set your TPS. Try to set it using the DVM method off the TPS pin directly. See your manual.
Pin 2O of the ECU is the switch solenoid output. With the key on there should be 12 vdc with your TPS in the idle position. When you move the TPS to half throttle it should drop to less than 2.0 vdc. Try to slide a dental probe or something in the back side of the ECU connector to make this measurement. Don't short it to ground!
When my resistor fried (both the 2O leg and 2P leg inside the ECU) I had 12 vdc on all three check connector pins (the one for setting the TPS). It's really easy to find inside the ECU. Find the 2O pin and follow the trace. The very first resistor is the one that burnt. The guy I mentioned in the post is VERY reasonable and accepts ECU's via UPS with a 1 day turnaround. Call his 800 # first and ask for Don.
I'm not sure what you mean when you say adjust your idle and talk about connectors. On my 90 vert there is a single pin connector front drivers side near the battery. This must be grounded before setting your idle (accessories off). With your switch error you can't use the lightbulb technique to set your TPS. Try to set it using the DVM method off the TPS pin directly. See your manual.
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Jeff20B
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