Engine Car stalls after 10 mins of idling

90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
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Start the car and unplug the IAC valve. Does it stay running without surging ?

It could be a coolant temperature sensor. Have you checked that out ? The computer uses the IAC like a choke. ( kinda ). The most common way a computer controls the rpm is with the IAC. It's used in combination with variances in timing and fueling but I've found the IAC does just what it says. Controls the idle air. Now, your car shows lean before it shuts down and that could be from the idle air control valve opening all the way up to try and save the idle.

When cold the car is running in closed loop. It's depending on preset programming to make the car run based on temperature. When it hits a certain temperature it starts talking to all the other sensors. The o2 sensors aren't used when the engine is cold. If you have a bad o2 sensor or the harness is damaged it'll cause all types of issues. I had a car that surged and ran like crap until I found out the o2 sensor harness was grounding out to the k member.

I edited a lot of this post to make it a little simpler
 
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Maciasmarci

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May 19, 2021
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It does not stay running when I unplug the Iac. I also tried using an inline spark tester and hooked it up on the distributor and the spark looked more like a glow than a spark but not sure if that’s normal. Anyways I noticed that before it dies the spark wants to also die out (fuel pressure is good and fuel injectors are firing also). only codes that I’ve got are 34 and 85
 

Maciasmarci

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May 19, 2021
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It does not stay running when I unplug the Iac. I also tried using an inline spark tester and hooked it up on the distributor and the spark looked more like a glow than a spark but not sure if that’s normal. Anyways I noticed that before it dies the spark wants to also die out (fuel pressure is good and fuel injectors are firing also). only codes that I’ve got are 34 and 85
 

Mustang5L5

Put lubricant all over the balls
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If it stalls with the IAC unplugged, open the throttle a bit with the throttle stop screw. In fact, open it quite a bit, unplug the IAC with the engine running and lower the idle down by backing out the screw. Once you get it to a stable, but low idle, plug the IaC back in.

You’ll need to reset the ECU by disconnecting the battery for 15 min.
 
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Mustang5L5

Put lubricant all over the balls
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So with the IAC disconnected and the idle screw in all the way, what is your approximate RPM?

Can you back the screw out and lower RPM? If so, at what RPM does the car want to stall out out?

I'm trying to determine two things. Can you maintain idle in the general 600-900RPM range without the use of the IAC, and secondly, is the IAC functioning in trying to maintain idle.

The thing with messing with the throttle stop screw is that it messes with the ECU and TPS setting. Now, the TPS just needs to be in the 0.5-1.25volt range at idle, which is a pretty broad range. Each time you adjust the screw, you really need to reset the ECU so it can relearn idle again. You should also dump codes and see if a code 23/63 is present which would signify the TPS is out of range.
 
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Maciasmarci

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I’ve reset the tps and did base idle reset w/ screw adjustment and still the same. Only codes I have are 34 and 85. What I also tried is unplugging the maf while the car is running and it didn’t stall on me then. Only issue is that my afr guage then will start to read super lean.