Cold Idle Issues and Resetting the ECU

[Chebyshev]

I have a '91 iX and I'm trying to figure out an issue with how it idles when cold.

The car will start and idle mostly ok around 600 RPM, but when I give it a little throttle and then let off it won't come back to a stable idle well, but rather the RPMs fall down below idle and sometimes it even stalls. Once the car warms up this is not an issue.

I tested the coolant temperature sensor and it is fine (and was replaced in 2019).
I've done all I can to find vacuum leaks and can't find anything (spraying carb cleaner, using my pickle jar smoke machine).
TPS is working properly.

If I reset the ECU (disconnect the battery for a bit), the problem goes away for a couple days, but slowly starts up again.

I read this thread:
https://www.r3vlimited.com/board/for...-it-run-better
It makes me wonder if I have a leaking injector or something that is making the engine run rich and the ECU tries to compensate over time, but winds up leaning it out too much to idle well when cold. Does that make any sense? If that's the case, how can I figure out which injector it is?

Anyone have thoughts for me?

[ADEN]

Your car idles at 600 rpm when cold?

[Chebyshev]

Your car idles at 600 rpm when cold?

Around that, yeah. Does that point to some other problem?

[ADEN]

On a cold start my car idles at not less than 900 rpm.

First check your coolant temp sender on thermostat housing (google the resistance of the sensor) replace if out of range.

Second ICV remove it, it should click when wiggling it to make sure it is not stuck, clean it and check resistance (google the resistance of the sensor) replace if out of range.

Third test TPS idle switch for continuity when throttle closed and discontinuity when throttle begins to open replace if out of range.

Good luck..

[Chebyshev]

I checked all of those things (ICV, TPS, CTS) last week.

Today I smoke tested it again with a better machine and saw nothing. Also tried a different AFM. No change: after resetting the ECU and driving for a while the next cold start was the same deal.

I'm getting a little frustrated.

[ADEN]

Try disconnecting the battery and the O2 sensor for a bit then reconnect battery and leave O2 disconnected and see, maybe O2 sensor is sending wrong data to DME causing your problem next start.

Cold start idle at 600 rpm is a problem too check throttle body stop screw it should be screwd to open the throttle just a crack (as per the Bentley) if adjustment is done to this screw adjustments to the TPS is needed.

[Chebyshev]

I remember reading somewhere not to fiddle with the throttle stop, but maybe a previous owner did?

What should I look for with the O2 sensor unplugged? Wouldn't that just make the car stay at the default rich map?

[Chebyshev]

I tightened the throttle body stop screw a little yesterday to create a tiny gap in the throttle plate. I didn't have a 0.0015" feeler gauge (that's super thin), so I used a piece of paper and made it so I could barely move it through the gap. I adjusted the TPS so it was still clicking at zero throttle.

Here's a video of cold start and a few revs from this morning: https://youtu.be/orlN-LikDR0

The noises at the beginning are me dicking around to make sure the radio didn't come on.

[ADEN]

I tightened the throttle body stop screw a little yesterday to create a tiny gap in the throttle plate. I didn't have a 0.0015" feeler gauge (that's super thin), so I used a piece of paper and made it so I could barely move it through the gap. I adjusted the TPS so it was still clicking at zero throttle.

Here's a video of cold start and a few revs from this morning: https://youtu.be/orlN-LikDR0

The noises at the beginning are me dicking around to make sure the radio didn't come on.

After watching your video again your idle is too low for a cold start fix this issue first. my car used to idle at 1.5k 5 years ago but for no reason now it idles at 1k but thats still acceptable.

If i were you i will give the afm idle air bypass screw alittle trun clockwise to allow more air that might fix your low rpm when cold, from the video your engine is struggling to keep itself alive.