Regal (1973-2004) Buick's sporty mid-sized sedan

1990 Buick Regal Fast idling on startup

Old 06-05-2019, 09:37 AM
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Join Date: May 2019
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Default 1990 Buick Regal Fast idling on startup

Hi all, I have a 1990 Buick regal custom with a 3.1 L V6 I have not owned it lang but do know the previous owner. The car had the ECM replaced a year ago and I just changed out the TPS after testing it and finding it was out of the range it was supposed to be. The car shows no codes and yes I have checked it multiple times. I have also gon over all of the tubings looking for vacuum leaks and all seems fine. I did find a couple that were marginal and replaced them. I also unhooked the battery and stepped on the brakes repeatedly to drain the electricity in the systems, to reset the ECM after the TPS swap. The issue is the car runs great but on a cold start up the idle is up to 1500 and takes 10 mins to drop to 800 then after running it for a while it hits the 500-600 range all the time. If I let it sit an hour or so the high idle starts up again. No stalling and as I said runs smooth and great once it gets past fast idle. Any clues on where I should look at this point? the car has just 56,000 miles on it sat in the garage most of its life was not used regularly.

Thanks for your help
Old 06-05-2019, 02:51 PM
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Join Date: Sep 2010
Posts: 811

Have you ha a chance to check out the coolant temp sensor?
If it is not reporting correct info to the ECM it will not throw a code for that. , but will affect cold start if not reporting the correct info to the ECM.
Old 06-08-2019, 07:30 PM
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Default Update

I ran the electrical tests and found the Idle air control was just slightly out of its range so I replaced it, reset the ECM by disconnecting the battery. I started it up and for the first time, no fast idle took it for a ride smooth as silk. Came out this morning and started it up and damn if it did not stall. jump up and down off of fast idle and then sit at fast idle for 8 mins before it started to settle down. Stalled two more times getting out of the driveway. I beginning to think the car is haunted. The previous owner had the ECM replaced about 3 months ago how would I find out if the ECM has all the updates on it? I ordered a new temp sensor and figure what the heck last of the sensors to be replaced. I also talked to the mechanic who worked on this he replaced the fuel pump and the fuel regulator because of stalling issues said it cleared it right up. I replaced the fuel filter today hoping tomorrow the gremlins are gone. Any other ideas welcome thanks for the help.
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