mazdaverx713b

iTrader: (91)

can anyone send me to a writeup or explain to me the adjustment process of the BAC on a gsl-se. i searched and came up with nothing. i have a FSM but it is 100 miles away where the car is and i will be with the car on wednesday and want a little heads up on this before i tackle it. the problem is the common idle surge followed by a high idle. i have a tps test light that i made and it works beautifully. i thought the problem was the tps coming out of adjustment again. i hooked up my test light and the thing was fine. i wanted to be sure, so i replaced the tps with another good tps that i had. same problem. high idle and surging at 1500 to 2500rpm. i inspected for vaccume leaks and could find none. this lead to me to speculate the BAC needing cleaned and adjusted. i know there is a screw on the side that adjusts the amount of air that will flow through and increase idle to componsate when the AC etc. is switched on. i am not sure how much to turn the screw or what exactly to clean on this part. i figure i can get the answer here. so, can anyone explain this to me or direct me to a writeup on this. perhaps i overlooked something when i searched. i did find however, some good explainations on cold and hot start procedures from LongDuck.......

Wankelguy

When I want to adjust my BAC, I can usually depend on Bourbon to get the job done.

mazdaverx713b

iTrader: (91)

bourbon eh? i depend on stoli and cranberry for a sophisticated evening but in this case, mgd and a naked woman don't help the bypass air conrtrol valve. they only make me long for 15 minutes ago where as we were... never mind. at any rate, i may need to ask LongDuck. or throw back some bourbon...

mazdaverx713b

iTrader: (91)

anyone know?

bizarro

iTrader: (1)

i don't remember seeing much to adjust on the BAC valve...i just took mine and cleaned it and it worked fine...

here's the site...

http://www.nellump.net/peri/epi/firs...gslseIdle.html

mazdaverx713b

iTrader: (91)

thanks hector, i'll look into it.

LongDuck

The dreaded 'surging' problem, eh?

I have done a few write-ups on this in the past, and would really recommend that you search for "Surging", "BACV", and "TPS" to find some good information on it from me, and from other posters here, but the gist is as follows;

The SE EFI system relies on butterfly valves and air bypass channels to get the proper amount of intake air volume during idle conditions. What you described about surging is usually due to a feedback loop that develops when one of the critical systems is out of adjustment or restricting flow. I'll describe a few of these systems, but the tutorials will help out with what you can do about it.

1) Throttle Body rods - these are steel and tend to stick in the aluminum TB when the lubrication runs out. If you remove the TB, you can run a thin oil along all of the joints where the TB and rods intersect. The problem occurs when the rods don't turn freely in the TB, resulting in delayed response, and starting off the feedback loop that causes 'surging'.

2) BACV - the Bypass Air Control Valve on the driver's side of the DEI chamber gets dirty through backflow air coming from the secondary and '6'-port air channels, so removal of the 2x10mm bolts and 2x connectors will get it so you can remove and clean with brake cleaner. Air bypassed by this control helps to maintain idle speed when you increase engine load through electrical devices.

3) TPS - the Throttle Position Sensor is what tells the ECU where you want the engine to be in RPM range. The TPS signal is combined with AFM readings to help the ECU decide how much fuel to inject. You already have the TPS light setup, so adjust this part to spec (one light on), and leave it alone.

4) Idle Adjust Screw - on the top of the TB, you'll see a small screw (flathead) that can be adjusted for idle air compensation - steady-state. This should only be adjusted for FINE idle adjustment, and usually only impacts idle speed if all other factors are working correctly.

5) Idle MIX Adjustment - Mazda term: Variable Rheostat - this is located at the passenger side strut tower, but is the LAST thing that you want to adjust when troubleshooting idle issues. This allows for Lean/Rich idle mix adjustment, but should only be attempted to increase idle QUALITY, not rpm. Idle mixture can help to smooth out the idle, but is useless to attempt to 'tune' with.

As I said, take a look through past posts and see what you can come up with. HTH,

riofrio

Can a faulty O2 sensor also mess up the idle?

LongDuck

Not likely - the O2 sensor is used during steady-state cruise conditions where closed-loop EFI mapping comes into play. Idle speed is totally driven through bypass air and AFM signal/TPS for off-idle acceleration, since you need slightly rich to promote increased rpm. The O2 sensor is not used during idle, IIRC - if someone knows better, I'm all ears.

What most people find is that heavy surging (500-1000 rpm or more) is usually mechanical, and slight surging (<500rpm up and down) is usually vacuum, BACV, mixture, etc.

First step is to clean the whole system up and get it running the way it's supposed to run, otherwise, you're chasing gremlins around and you'll never get it running right. Once it's done, though, it is a treat to know that you learned the ropes and know how to fix it in the future. It's a minor annoyance that you either learn to live with, or get used to 'retuning' every year or so.

My surging SE usually starts acting up when it cools off in the fall. This is due to the TB shrinking slightly against the butterfly rods and causing the mechanical feedback issue covered above. Removal and light oiling on one side, then the other, and it's back to perfectly smooth idle. HTH,

mazdaverx713b

iTrader: (91)

well, today i am off to work on my SE. i will try all mentioned above, oiling the TB rods and a good BACV cleaning along with a re-adjustment of the TPS. i'll report back and let you all know how things went. thank you for all of your advice!

mazdaverx713b

iTrader: (91)

ok, well i am frustrated and a tad discouraged. nothing worked. i cleaned the BACV and TB and lubed the rods and cleaned and checked for vaccume leaks. the idle is still at 1500rpm unless you push down at the screw that adjusts the tps. i replaced the throttle return spring and this did not cure the high idle. the idle still fluctuates 300 rpm at a time. the engine idles fine and does not start fluctuating until after the car is driven. the only thing i did not check was the vent solenoid valve. i rad about it but did not check as it was not mentioned much. any other help would be very much appreciated. thank you for looking.

web777

Double check your vacuum lines. There's ont that goes to the cruise control which tees off near the exh which typically breaks. Aslo there is a line under the UIM which hard to see.

bizarro

iTrader: (1)

if its not a vacuum leak i bet its the solenoid...get one from the junk yard and replace it

Northern 7

iTrader: (3)

This still sounds like TPS -
You can change out a dozen new TPS's and will still have the same problem if you have any binding in the throttle body linkage. Sometimes this is due to worn out parts that have loosened up enough over the years to throw yor TPS off every time you hit the gas - if there is any play in the linkage, your TPS will have a tough time finding its mark. If you are lucky, the linkage is just dirty and requires a good cleaning and re-lube - try that first and then look for play due to wear

mazdaverx713b

iTrader: (91)

i don't know if this will help but the problem occured after i drove the car on the highway. it was an hour trip averaging about 80mph. i have taken the trip twice before in the car and it covered the hundred miles both times with no problems. i guess i will have to try to replace the solenoids and have a closer look at the vaccume lines. i am not sure why i have to push down on the screw that adjusts the tps to get the engine to idle down. i cleaned and lubed the throttle body and still nothing.

riofrio

I've been having very similar idle problems as the ones you described. After I'm done changing my exhaust and O2 sensor I'll give it my attention again. Please let me know if (and how) you get any progress, I'll do likewise. Good luck.

LongDuck

When the idle is surging, as you look at the TB, can you SEE the butterfly throttle rods oscillating and turning? If so, you definitely should look back at the TB oiling procedure to get this fixed. When the rods DO NOT turn, visually, you're looking at a problem with the BACV and/or the connector that drops down and measures load from the alternator/ECU.

If the throttle rods aren't moving, you have a vacuum leak somewhere, so check around the DEI chamber and the BACV - it could be as simple as a damaged gasket connecting the BACV to the DEI. Also, ensure that your TB gasket is in good shape, along with the rubber phenolic spacer between the DEI and the TB. Any minor leaks here will cause fluctuating idle due to air pressure changes in the intake tract.

Also, check your brake booster line to make sure it's sealing well - a breech here will open up another intake system leak that could cause 300 rpm surging.

If you push down on the TPS adjusting screw and the idle returns to 800-900, you may just have not run the engine up to operating temperature, first. The Fast Idle Cam will keep the throttle at 1500-2000 until the coolant comes up to temp, so these adjustments should only be made on a WARM engine - should have mentioned that before.

Keep at it, it's not rocket surgery, and you've got plenty of help from us here,

RX7Rox

I too had the same problem on idle fluctuating after a drive. I caused the problem tho when I thought I was doing something good, was actually bad. I wanted to remove all the gum and varnish from all the t/body linkage, levers, springs and rods. You know make it all pretty and clean. What I did was removed all the lube that made everything operate freely. So my secondaries would stick and not close all the way. I could move the lever with my hand and make the secondaries close and it would idle fine. I believe this was allowing too much air and it was trying to compensate hence the fluctuating. There was even a Mazda TSB about this problem, but the cure was replacing the throttle body. I don't think so! Bought a airsol can of Marvel Mystery oil and lubed up the shafts and linkage and has been working fine since.

revn247

Funny you guys mention lubing up the throttle linkages. I've never done it. I steam clean the engine regularly too....No issues w/ cold start up or hot running. No major oil leaks.
As for the surging problem: check/adjust the TPS. 90% chance.
Next check the cold idle cam associated linkages....could be just stuck in the cold idle position. Which could explain why you cant push the butterflies closed. David Lane has a really good write up on it...I just dont have the link available to me. Maybe someone else has.

mazdaverx713b

iTrader: (91)

thank you all for the info. i won't give up, i'll keep on keepin on!

mazdaverx713b

iTrader: (91)

for note, there was oil in between the throttle body and the plastic spacer. hmmmmm...

LongDuck

Yeah, that can happen. Remember that when you back off the throttle, you have the '6'-ports that should normally come closed to block off the return path for air to get from the combustion chambers to the DEI chamber.

If your '6'-ports are stuck (open), or sticking when they close, this bypass air from the combustion chamber will go through the separate passages in the upper intake manifold and DEI chamber and allow oil to be drawn back up this path from the oil injectors. Normally, this isn't a problem, since the butterfly valves would be open on your secondaries ('6'-port inlets) to draw the oil into the engine, but it's not uncommon to find oil in both the DEI chamber and even the Throttle Body phenolic spacer. It shouldn't be able to get much further upstream than that, however.

Keep looking - that's not the problem. Good luck,

riofrio

I've replaced my TPS and I keep noticing the same thing: I'll hook up the test lights (which work well), and they'll both be off. So I turn the screw clockwise, and one of them turns on. So then I I keep turning cc, just to have an idea of the amount of range that i have, but I will never see both lights on. I have turned the screw cc all the way, and never seen them both on. I've even pushed the TPS all the way in with my finger and still, never seen both lights on simultaneously. I don't know if this means that my TPS is bad, or if some of the connections are.

LongDuck

OR your bulb is burned out on your test rig.

riofrio

well, I've switched the bulbs around and made sure they both work.