Stalls Once Warm?

Hello my name is Colton
I have a: 1991 3000gt
My GT has a strange problem that we cant seem to find the solution for it will start up and turn over all day long if you start it while it is cold it will turn on and run. Its drivable and everything for about 10 minutes, after those 10 minutes are up and the engine is warm it seems that the rpms slowly sink all the way down until the engine doesn’t have enough to continue working. After that point the car stalls once it stalls it is possible to turn the engine over again if you give it gas and keep the rpms high. just by giving it more gas it will continue to run. I just recently bought the car so I’m not 100% certain about the history of the vehicle but it seems fairly well taken care of. The things that have been replaced and checked so far have been the battery we looked into the crankshaft position sensor but ultimately couldn’t locate it on the actual vehicle the IAC could be a possible problem or maybe the ECU I’m semi new to actually working on vehicles so I thought I would get some other opinions

The crank sensor on a senor is part of the cam sensor. They are both in one unit on the side of the rear head.

I would say your issue is the IAC.

Quick and dirty test is to OHM it out. There are six pins

Imagine them like this


You’ll check resistance between 1-2, 2-3, 4-5, 5,6. Resistance should be around 32ohm if its an older brown top one. It will be around 40ohm if its a newer black top one. If you get 0 or infinite resistance on any of the tests its bad.

1 Like

Also a quick note, your car is now 31 years old, it is a good idea to send your ecu in to be rebuilt as the capacitors are all expired, they’ll be prone to leaking and will cause damage to the circuitry.

At the age of the car I’d say the capacitors have already been changed.

Could it be fueling? Could be wrong but doesn’t the fuel pump get more voltage while the car is warming up , maybe the pump is weak and when the voltage drops its unable to fuel correctly. I think you can hotwire this by bypassing a relay under the air fiiter.
Sorry if this is unclear, I’m just trying to recall research I did because my car has always had the exact opposite issue, its lumpy and will stall if you try to drive from cold but if you let it warm up for a few minutes, ( I’m going to say 10 but maybe less) it drive perfectly. I haven’t spent much time on it because its not that big a headache, I’ve always let my cars warm up before use.
I can hear the change in the sound of the engine when she gets up to temp also ( like when the choke goes off).
I’ve always suspected fuel so just thought I’d mention it.

I will definitely check the ohms later and thank you for the info on the sensor.

I pulled the ECU last night and popped it open to take a look it looks like someone tried to change the capacitors but did a really horrible job it looks like it was probably their first time ever with a soldering iron!

I will make sure to check that out it would make sense.

I used to have the exact same problem, and I kept everyone updated with it on here, as it took me forever to get to figure out what it was.

Long story short, for me it was CAS (Crank Angle Sensor), If yours is a 1991 with DOHC then yours will only have one sensor and its positioned at the top near the Throttle Body.

Good guide here:

1 Like

Id send in the ecu to a proper repair shop. Hopefully they can clean it up. The sloppiness of the replacement capacitors could be your culprit. Hopefully it didn’t cause the circuitry to become damaged.

Any suggestions as to where to send an ECU in the U.S. to have it competently rebuilt? Thinking this may be a good idea for our 1994 model.

(888) 593-2262

I sent my firebird ecm to them to be repaired, it was beyond repair and they sent me a remanufactured one to replace it.

They did not communicate well after I gave them the ok to find a replacement; after a few weeks had passed sense i have them the ok, I emailed them asking for an eta.a couple more weeks passed and I started to look for an ecm elsewhere, found one and ordered it and 3 days later received both ecm’s (one from the one I ordered elsewhere and one from module experts). The one they provided has all new capacitors and things that all ecms need to have replaced. My takeaway is they’re good price and good work, but not very effective with communication unless they need your authorization for something. I’d use them again, but I won’t bother looking for updates from them.

There is a guy on the facebook forums who rebuilds all the ecu’s for these cars. I can get you his name if you want. He does very good work from everything I hear about him.

That would be great. Please send me the info.

This is the guy, send him a message. I think he has a website too but I cant find it on his facebook profile. Any time an ecu needs to be rebuilt people always recommend him.