I have a 1988 GT, 25k miles and have been trying to figure out the problem when starting and also accelerating between 35 to 50 mph.
When I cold start the car it starts right up, runs 3-5 secs then chokes and stops. I start it again and the same thing happens.Then on 3rd try it starts,
runs, RPMs lower to about 600 but will stay running. Also, I've noticed at around 30-40 and accelerating, the car studders oh very slightly. There are new
plugs and cap that were installed last year. I've thought maybe it's the Idle Air Control valve, but before I go and replace a bunch of things, I thought
I'd ask on here as I've always had good luck from members. Anybody with suggestions?

[This message has been edited by mnsportsguy1966 (edited 07-21-2022).]

Someone else may be able to chime in with a bit more info, but when I had this issue I found that there are a LOT of sensors that can cause issues with idle and drivability. There are instructions on here about how to test almost all of them. I would look into how to test IAC, IPS, Coolant temp sensor, o2 sensor, and intake air sensor. These can all mess with how the car runs.

quote Originally posted by mnsportsguy1966: Then on 3rd try it starts, runs, RPMs lower to about 600 but will stay running. Also, I've noticed at around 30-40 and accelerating, the car studders oh very slightly.

600 RPM is too low. Sounds like the TB idle screw setting is doing it's job because the IAC is not.

Testing the IAC.
https://www.fiero.nl/forum/...090907-2-090637.html
https://www.fiero.nl/forum/...030819-2-033773.html

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3.4L Supercharged 87 GT and Super Duty 4 Indy #163

[This message has been edited by fierosound (edited 07-22-2022).]

Might want to inspect the pickup coil as well. Easy, just pull the distributor cap and see if it's disintigrating.

⚠️ Warning: If the IAC is out of TB/TBI and connected to wiring and turn On I-key then can wreck the motor. More so w/ A-B shorted to "close the valve" as other half isn't there.

Could try IAC links above... may not help.
Get a "noid light" for IAC. This light "replaces" the motor to see if ECM turns on/off/blinks the 2 lights.

If light does nothing then likely have a problem w/ ECM or wiring.

"low mile" 30+ year old car can have heat related and other problems w/ iffy ECM.
Solder joints can crank open.
Old GM OBD1 ECM can have a factory defect.
Either/both can happen when hot, cold or always killing part to whole ECM.

If ECM is "Dead" must save the PROM/MEMCAL inside to move to new ECM.
also See my Cave, ECM Heat

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(Jurassic Park)

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Hey everyone thanks for all the input. At this time I still haven't gotten it corrected. It still takes 3 times to get it to keep running on cold start
and it still jerks when driving 30-40 mph. I did actually bring it to a trusted shop and they said the fuel pump was weak so they replaced it and
also found my fuel filter was dripping and changed that as well to no avail. It bugs the heck out me to know it still isn't running the way it should
and hate bringing to an Auto Repair Shop cuz it gets expensive. I haven't tried everything that has been suggested as time is short doe me right
now. Any more suggestions are greatly appreciated.

Pull the plugs and post pics, maybe iffy injectors ?

quote Originally posted by mnsportsguy1966: Hey everyone thanks for all the input. At this time I still haven't gotten it corrected. It still takes 3 times to get it to keep running on cold start and it still jerks when driving 30-40 mph. I did actually bring it to a trusted shop and they said the fuel pump was weak so they replaced it and also found my fuel filter was dripping and changed that as well to no avail. It bugs the heck out me to know it still isn't running the way it should and hate bringing to an Auto Repair Shop cuz it gets expensive. I haven't tried everything that has been suggested as time is short doe me right now. Any more suggestions are greatly appreciated.

Sounds like they had no idea and were just throwing things at it. Can't imagine it was the fuel pump.

Remove the IAC, clean the pintle and the IAC hole and replace it. IACs generally are tough, but it wouldn't hurt to make sure the pintle and bore are clean and free to move.

Note - DO NOT extend the pintle when the IAC is out of the throttle body. If you do when it is reinstalled, the pintle can bottom out and the IAC can be destroyed.