Challenges setting minimum idle air.

[scorp508]

I've been chasing a situation where my engine stalls when cold rather easily, as well as when the engine is warm if coming to a quick stop.

According to TunerPro RT my IAC steps were ~60 at idle once the car is warm. This seems a bit higher than others here have suggested it should be.

The first thing I did was remove my IAC and clean the pintle and bore.

Before/after. Yes, the O-Ring was put back even though it isn't in the after shot.
IMG_7703.jpg

IMG_7687.jpg

I then attempted to go through the procedure to set minimum idle air and reset the IAC here: https://zr1.net/forum/showthread.php?t=27764

All was going well, but in step 6 my throttle stop screw was basically already turned in (clockwise) as far as it can go, so my understanding is I have no adjustment left to "lower" the minimum idle air. It was a hex head screw, 8mm I believe. Have any of you had to get a longer screw?

This was after messing around with it a bit trying to back it off. When I started the nut and screw head were both all the way in.

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Interestingly if I let the engine run the idle would start around 1200 (ECM's commanded desired idle was 850), then start climbing in small increments and slowly run away. In other words, it would start at 1200, then 1250, then 1300, etc. and keep climbing until I killed the engine. Vacuum leak? I don't understand how with the IAC unplugged and the throttle body blades not moving the engine was able to gain so much RPM. The TPS was at 0.53v the whole time. Wondering if I should smoke the intake and look for leaks.

The car does idle dead nuts where the ECM wants it, but was hoping to get IAC counts down and improve this stalling situation.

All ideas are welcome.

[Mikey]

I am confused. You describe trouble keeping idle and high IAC counts followed by surging rpm that seems to be air leak related.

[scorp508]

Sorry I probably could have laid it out better.

Before doing anything.

1. Car holds ECM commanded idle speed great. IAC shows steadily around 60 steps at idle once warm.

2. When cold, car stalls when coming to a slow stop nearly 100% of the time.

3. When warm, car occasionally stalls only when coming to an unexpected hard stop.


While trying to set min air via stop screw and IAC disconnected.

1. Can't get idle low enough via stop screw. Screw is already turned inward as much as it can physically go.

2. After about 20 seconds of engine running the idle begins creeping upwards with no end in sight until I kill the engine.


Put it back together as I had to go pickup my son at daycare, and did the final IAC reset steps even though I wasn't happy with it yet.

1. Car holds commanded idle.
2. IAC steps now 80. My stop screw is not "as closed" as it was when I started, so this sort of makes sense.
3. No apparent runaway idle increase.

[XfireZ51]

Did u plug in ALDL, TURN IGNITION ON, then unplug IAC first? The. Unplug ALDL B4 turn off ignition? This closes off IAC port.
Also, throttle blade closes as u back out set screw. At 60 counts, most of the idle air is going thru the IAC.

[scorp508]

Originally Posted by XfireZ51

Did u plug in ALDL, TURN IGNITION ON, then unplug IAC first? This closes off IAC port.

Yes, I did. To confirm I did the right thing, I pinned the ALDL pins used to show the CCM/ECM/ABS/etc. codes on the dash. I did see the code reading process start before I got out and unplugged the IAC.

I could remove the IAC again and confirm the pintle is fully extended before moving to the next step, unless that runs some kind of risk.

Also, throttle blade closes as u back out set screw. At 60 counts, most of the idle air is going thru the IAC.

Now it is closer to 80 with the screw backed out more than it was before. Hmm. I ordered a smoker to see if there's a leak somewhere, should be here on Friday. When I have more time to do this I'll go through the entire procedure once more. I was sort of rushed by having to quit and pick up the kiddo yesterday.

I don't know if this matters, but at the point where I was going to adjust the stop screw with the engine running I did have TunerPro RT datalogging via the ALDL to get a better read on RPM than the dash itself.

[XfireZ51]

Originally Posted by scorp508

I don't know if this matters, but at the point where I was going to adjust the stop screw with the engine running I did have TunerPro RT datalogging via the ALDL to get a better read on RPM than the dash itself.

I unplug IAC w Ignition ON but not started. Then go back and turn OFF ignition. I do use my datalogger to check RPM. U should turn throttle set screw until idle is slightly lower than the desired idle speed. That way the IAC will intervene(when everything is plugged back in) to raise idle to desired. I usually do this after the fans kick in so as to have an additional load on motor and an additional margin of IAC counts before finalizing.

If u have IAC counts, that would indicate no leak especially w 60. The IAC is doing all the work of keeping the motor idling.

[scorp508]

Originally Posted by XfireZ51

I unplug IAC w Ignition ON but not started. Then go back and turn OFF ignition.

I did the same.

I do use my datalogger to check RPM. U should turn throttle set screw until idle is slightly lower than the desired idle speed.

That's the step I was on, but the idle started creeping without me making screw adjustments. I'll give it all a go again when I have more time on hand.

[scorp508]

How far should a fully extended pintel be? I'm measuring 17.6mm from the tip to the black casing just before the o-ring. Closer to 27.5 if I measure tip to the flange that mates against the TB.







This looks like close to 28mm to the flange is accurate. I just tried again and even with the screw fully backed off I can't get it below 1200 rpm when commanded to 850, but if I button it all up it idles nice and low.

[XfireZ51]

When u connect ALDL, turn ignition ON, how many steps are showing for the IAC using ur datalogger?
One other thing to try is take IAC OUT and plug IAC port to seal it. Make sure the IAC IS UNPLUGGED b4 trying to start motor.