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Pontiac Repair/1990 pontiac grand prix reving and speedometer problem


I have a 1990 Pontiac Grand Prix that has not been driven for about 6 months except to be moved little way. It runs like a dream. No miss or anything but revs when started and dies but only when warm. The tach and speedometer always reads at least twice what it should. We have tried changing iac and throttle sensor. What could it be and would the ecm make the speedometer and tach go nuts? There is no carbon build up that I can find. have also put fuel injector cleaner in it. Please help as my van blew up and need to use this car now. Thanks. It is a 3.1 6 cyl. le

Hi trudy.

That year car is a noted for bad ecm's. a classic symptom is the speedo wacking out and stalling. So I would say your right in your guess. If you choose to replace it your self do a goodle search for 3.1 Liter idel learn proceedure. If you don't follow it the idel will be erratic and you will have stalling issues with the new ECM due to not learing the idle speed. good luck :-)

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Todd Puccio


General auto repair,electrical issues,driveability issues,anti-lock brakes,SIR systems,HVAC,engine performance,Gm specific. I have worked at my current dealership since the 1990 model year anything much older than that I have limited exposure to. I do not have very much transmission experience so those question you may want to ask of another expert. When you send me a question let me know the exact make/model/engine and year for the car or suv you have it makes it easier to answer the questions that way. If your happy with the answer I gave you please feel free to Donate. This is a free service to you and I am not compensated at all by this web site. I have 22 years of experience to share with you and my knowledge wasn't free to me. I had to pay for my education.


Experience in the area: I have been a technician in GM dealerships for over 22 years and I am a ASE master technician. I work at a Buick and GMC truck store Previously I worked at a Pontiac GMC store for 18 years. I Served a a lead technician when dealership was on a team system. I just recently moved to a Buick,Hummer,Saab Store when my franchise was purchased by this dealership. Organizations: ASE master technician


Education/Credentials:High school diploma,2 year vocational school degree 2 year college degree. Associates degree in applied sciences (auto technology)Awards and Honors: GMC master technician

Awards and Honors
Master GMC truck technician Master ASE technician in 9 categories

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