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

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.

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.

Perhaps throttle position sensor? Maybe talking about same thing, would determine speed through gas pedal and if erratic may cause conditions as stated when motor is cold. Wait, 1990 may still have throttle cable, single point fuel injection and throttle body? If so- same difference, used to all be done mechanically and now electronic......

Once in awhile even answer years old posts lmao.

At this point after several IAC controls swapped out all ACDELCO. Ran the full by the book retrain on the ECU with the same results the car runs well after all the work then reverts to the fast idle on startup. I have replaced the TPS twice and the temp sensor once both on the meter read spot on. The IAC is where the fluctuation occurs I did check the tree lines for possible shorts and all show clean from the sensor to the ECU no continuity to the engine or the frame. So I have ordered another ECU and will give it a try. I would like to ask has anyone found an issue with the chip and can it be replaced without having to reprogram? None of the Buick dealers in the area has any equipment or techs with knowledge on that, so they say. All refuse to try and service it at this point. Did find a local mechanic but he no longer has the equipment as well.

Roger that on repairs and thorough troubleshooting. Wouldn’t have mouse nest or hoard under air filter? I did but not to the point of any troubles. Found my old timing light and dwell meter up on top shelf in garage, alot of dust after 30 years. Believe cars from the ‘90’s may still be able to use some of the more conventional test techniques; can’t recall for sure or even know if Buick.

If engine had a hard time with air flow, would auto idle faster perhaps? Everything looked at would be past air entry before filter so far it seems.

If this is of any help,
The ECM has what is called a PROM chip in it. PROM= Programmable read only memory. We don't program them , they come from the supplier already built.
The integrated circuit chip is removed from the old ECM and installed in the replacement ECM. The replacement does not come with the chip because the chips are programmed according to what vehicle they will be installed in. Each vehicle has a PROM code and the test equip will always tell you what code chip is presently in the computer (ECM).

I don't know at this time because I cannot see the vehicle, however, the system is designed to add fuel (increase injector pulse width) according to how much air is coming into the engine. A vacuum leak that diminishes when the engine gets warm could be one cause. If the IAC (Idle Air Control) valve is not working correctly when the engine is cold could also be involved. You didn't state if there was any check engine light.. If there is, need to get the code(s) stored in the computer. Easy to do , only need a paperclip to do it.

I still own a 1990 Buick Century 3.3l engine . One of the best Buicks I ever owned. Had many before this one
Compared to the newer Buicks, it is a GEM.
Rich B.is The guy to go to , he does a heck of a job on this forum, Thank you Rich.

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ok, let me start with the basics of what has been done to the car in the last three months. Fuel pump, sending unit and screen all replaced (ACDelco) new fuel filter (ACDelco) Temp sensor, TPS (twice ACDelco) IAC 4 times (ACDelco) ECU replaced with a Cardone remanufactured, New control module (US made) 3 new coils Plug wires and plugs all (ACDelco) and a new Fuel Regulator. The car has never shown a code I do have the OBD1 hardware from GM. We used Propane to check for leaks found a slight leak in the vacuum line to the climate control and repaired.

The car after each change out the ECU was reset following the GM procedure battery disconnected 3 mins reconnected the car is started put into drive car runs til radiator fan cycles on and then off Car is shut down and repeated. It runs fine no racing no stuttering smooth as if new. Next morning come out try to start hard starting and rough idle then off to the races RPM up over 1500 on Tach. settles a bit shifted into reverse or drive car stalls restart hard starting then off to the races again 1500 RPMs. Verified wires from the IAC were not pinched or broken or shorting out the meter says they are clean. Car running initially looks fine then next day fluctuations in IAC meter reading coming from IAC as if bad or ECU is running to find a proper setting.

Moving on new ICU from GM due in tomorrow. If this does not do the trick I am tempted to get a new EPROM just concerned about getting one that will work. I can buy a blank the issue is reprogramming it to the car specs if the original is bad. Was hoping someone had tried that if so with whom did you go to?

Thanks Hanky but we know you probably forgot more than I ever knew. Can’t come up with any better than your overview. Recall my C4 Corvette was able to upgrade with a PROM. Was like they call a tune these days back then. Chrysler in ‘84 had to change complete computer. One thing I was never sure of was with that, had to install a 160 degree thermostat that came with program. Allowed engine to run cooler? I also understood engines should run hotter for maximum efficiency. Know back to road runner days before that even the 160 wouldn’t let the engine get hot enough on winter days, no heat lmao.

Forgot, if even one of those PROM tiny legs/pins is bent, not seating- the thing probably won’t work. And yes, they only go in one way; like being polarized, but will fit either direction. Usually have dots, indentions for direction.

Dont know either when OBD 1 was upgraded to OBD 2. May be using wrong tester?

Hi all, Thank you for your help thus far here is an update. I ordered a new ECU this one did not come from cardon and is a genuine GM remanufactured. I put it in and then ran the full reset started the car put it in drive with my foot on the brake and ran it about 10 minutes till the cooling fan ran and shut off at the radiator. Shut it down and restarted it and it was better ran it tor 7 mins till the cooling fan ran and shut off. It seems way better but tomorrow will tell. I did get a stutter when I drove it after the reset and it now stutters as I give it gas just a bit then runs like a champ. Did I say this car has only 60,000 miles on it. I know I replaced the fuel pump and the fuel regulator because the pressure would not hold in the rail after I shut it down it would slowly drop. I thought I had that issue resolved but know I think I may have missed something. I am leaning to either the pump is a bad one (it was new ACDelco) or should I be looking at a bad fuel injector. Any help or suggestions would be great. If anyone can read their manual mine is old and well has some grease on it and I am not 100% sure what the pressure should read at the rail port when running. If you have one and can take a look and post it that would be very helpful. I will keep you updated. Thanks Again

Boy, if that doesn’t sound now like with carbs, faulty accelerator pump. Req’d extra shot of raw gas along with any increase of air velocity. Cars would hesitate and falter for a few seconds with hard speed up/downshift for going faster. Translated to today’s cars, Hanky has the best plan on that I’d say. The throttle body butterfly self adjusts for cold start, acceleration with gas pedal, fuel enrichment pulse duration of injectors. Hand chokes worked perfect as long as you didn’t forget to push them in after warmup lol.

Everything is different today but the same I guess you can say. Even TV’s now a days. Still use my 50 year old rotor (like new), 30 year old VHF/UHF antenna (on roof), amplifier and of coarse big digital TV set. Picks up free air signals- way too many channels and doesn’t cost a cent. The rest is free streaming via Amazon Prime, works for me. Won’t have cable or satellite, could never recoup the costs?

oh too, the switch from 80MM to 84.5MM throttle body on my Boss Mustang works exceptional. Power gains, haven’t noticed a lot; wasn’t expecting to, all old news anyways.

Hey Hank thank you. I did double and triple checked the IAC per the instructions in the manual the pintle was under 28mm. it would not move out to 28 but since the instructions said nothing about being under 28 I thought it was ok as the learning would move it in and out. All three I tried including the last one in the car were all AC Delco from Rock Auto. Any more advice welcome.

Since I replaced the ECU last night and ran the train per the GM instructions it ran ok last night. This morning it was hard to start and ran like crap and every time I tried to put it into reverse it stalled. When I finally got it out of the driveway and put it into drive it was racing again but settled down as soon as drive engaged. it also stopped stalling when I put it in reverse once I drove it to the end of the street and back. Running short on Ideas on what to look at again the fuel rail pressure is 40PSI and it holds. Wondering if it is a clogged injector or two. The car is 29 years old with just 60,002 original miles thinking when they started it the first time it may have swallowed a load of junk and the screens are toast. Do you have any thoughts? 3.1 Liter V6

Hey Rich, I too have a 1990 Mustang LX ragtop 25th anniversary edition that runs like a top with the 5.0 got just 80,000 miles on it, wishing the Buick was as easy to work on as my pony.

Very nice EDQ, a few come and go by every so often and this one green fox body.... running very strong, hear him coming from 1/4 mile down the road, he’s running some horsepower.

Ok, an update and a question. I rechecked all the vacuum lines still can not find a leak the throttle body on top has the connection for the three main vacuum lines the rubber plug looks a bit worn so I tried some permatex ultra-black on the three plugs to see if they were actually leaking air. But no real change. I did double-check fuel pressure but I am a bit concerned about what was up. When I first put the gauge on it this morning I got zero reading no pressure I turned the key to on and got 40PSI steady from the pump. I turned it off and watched the gauge for an hour and it lost about 1 PSI. The car still runs like crap on startup and after it settles down has a solid hesitation when you go to give it gas then all is fine. Got me scratching my head not sure where to look. Car mileage sucks and you get a whiff of gas right after you start it but nothing on the cardboard I put under the car last night. I did put a new AC Delco fuel regulator on it 2 weeks ago new fuel pump in the tank and a new fuel filter. Any suggestions on where to look next would be greatly appreciated. One last thing if I disconnect the battery run the car in drive till the fan turns on and cycles off then shut it down restart and do it a second time the car runs much better till it sits overnight next day the same old racing and stalling.

Thanks, Hank will give it a go and let you know.

Hi Hank,
Followed your instructions to the T. When I turned the key back to the off position with the IAC still plugged in but not mounted the plunger shot all the way out. I was able to get it back in without a lot of effort. I did the procedure again but after it set I unplugged it then turned the key off and mounted it. What do you think IAC may have been damaged I ordered another The car was hard starting but finally she stayed running ran it for 15 mins through 3 full cycles of the radiator fan about every 4-5 mins she would stutter but never stop running. After 15 mins I shut it off and restarted the rpms jumped at first and she bucked a bit but settled down to 1000 RPMs and steady still high but down a lot from the 1800 rpms she was cranking out on startup. Never touched the gas. Any thoughts?

I may have given you some inaccurate info on installing the IAC.

I believe it should have read , the pintle should extend out about 1 in. and if more, lite pressure can be used to push it in to that dimension, then install it. It is not recommended to plug or unplug the IAC with the key on.
After installation, turn the key on , don't attempt to start the engine, then turn the key off. This step is supposed to allow the IAC to reset . Then start engine and allow engine to settle down to correct idle speed. Shut down engine and restart it should come to the correct idle speed.

If there is any way for additional air to get into the engine like a vacuum leak the IAC will have to account for that and set accordingly. but in the meantime the result will be a high idle speed. It might be a good idea to check for possible vacuum leaks.