Stalling when coming to a stop


So my '91 GTO TT has got a issue where occasionally when I press in the clutch coming to a stop to swap gears the car will just die and cut out.

Revs drop to where idle should be around 700 then jump down to around 200 and sometimes will cut out and other times bounce back up.

I have recently fixed my Tacho so can see what RPM the car is doing and at a cold start the car idles around 1800 and drops to around 800-900 after a few minutes.

My thoughts have been a vacuum leak or potentially the idle control valve? Has anyone had any similar issues previously with their car?


I had the same problem in my '94 VR4. My problem is that I live less than 3 miles from where I work. These cars need to be run. My mechanic told me to put in fuel line/injector cleaner and take the car out and run it at highway speeds for at least 30 minutes. Give this a try. It worked for me and cost less than $10.

Your issue is likely the IAC on the throttle body. You can test it out by ohming it out.

There are 6 pins (2 rows of 3) you’ll check resistance between the neighboring pins 1 to 2, 2 to 3, 4 to 5, and 5 to 6. They should all be around 32 ohms. If there are any way out of spec it’s bad.

Cheers will give this a try this weekend

I have the exact same issue but mine is an N/A

Have tested the ECU, Coil Packs, and VIC, replaced MAF, IAC, and Spark Plugs.

Still got the issue.

Have bought some injector cleaner but not had a chance to try it yet.

Check your PTU/igniter.

Will do thanks, recently changed it however unsure if the car did it previously as just recently got the car and changed the PTU to see if it resolved the tacho (which it didn’t it was the capacitors on the tach).

I still have the old PTU so can try that as well

Mine only has 4 pins on, seems to be working fine though.

Found a vacuum leak next to the inlet manifold where all the vacuum lines connect there is two lines missing they seem to be tucked behind tied together and blanked off. The area where they connect has not been capped so unsure if this is causing the issue need to get hold of a manual but believe the reason it is like this is the previous owner fitted a BOV.

So measured the resistance on the IAC (measured the wrong plug last time) and it was 39.2ohm across all the pins, fitted a new IAC and connected the vacuum hoses all up correctly, and now drives spot on

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So may have been a placebo, issue has come straight back unsure if I’ve just bought a bad IAC.

If anyone has any other thoughts on this would be appreciated. Only issue is when coming to a stop and having the clutch in it fluctuates between 700-200 rpm and occasionally stalls

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does it happen when the engine is cold? or happens when it has warmed up a bit?

Only happens when warm

Have you ohmed out your injectors yet?

Not yet will give that a go this weekend should be around 14 I believe shouldn’t they?

Something like that. I think the bigger issue is if there’s one that’s wildly different to all the rest.

I see, ok I used to have the exact same problem. It would stall after it had warmed up. And sometimes would not run again untill I left it for a few hours.
I have a thread on here on what I went through untill I got to the source of the problem.

Long story short, it ended up being the CAS (crank angle sensor). Change that and car ran perfectly!

I’ll find the thread and send it to you. There is another thread online that shows how to change it properly. (That’s if you’re is a DOHC)

This is the thread:

Mine is the DOHC, however never had an issue with starting it always starts up straight away and has no issues after it dies.

I’m trying to wrap my head around it as it didn’t do it when I got the car but have a feeling it started after I swapped out the PTU hoping that it would fix my RPM gauge (It didn’t I ended up soldering some new capacitors on the dash) so I feel like there would be no harm swapping the old one back in not sure if that would be related.

Going to pull the plugs and swap the PTU next weekend see if that tells me anything and go from there

Where did you buy a CAS from?

From the breakers yard. Autoworld based in Leeds (UK) they brake lots of GTOs. Unfortunately the main guy, Graham is no longer with us.