it revs up and down erratically and sometimes it just stalls

2001 PONTIAC GRAND PRIX

190,000 MILES • 6 CYL • FWD • AUTOMATIC

STEVEWEIDERT

MEMBER
1 POST

I have the aboved mentioned car. On start-up it starts hard sometimes and once started, it revs up and down irratically and some times just dies. The Mass Air Flow sensor is good, the Throttle Positioniong sensor has been replaced. This car has 190,000 miles on it. What is possibly causing this behavior? Thank you

Mar 31, 2011 at 5:44 PM

SQM

✓ASE Certified Mechanic
6,383 POSTS

Hello,

It sounds like you could have an issue with the idle air control valve (IAC).
A dirty IAC can trigger issues with the vehicle idling.

Over time larger air particles will stick to the inside of the valve. And it can restrict the air flow. With a restricted air flow through the IAC the engine will have poor idle.
Many times servicing the IAC by cleaning it does improve the idle quality.

Here are some helpful articles:

https://www.2carpros.com/articles/how-a-idle-air-control-valve-works
https://www.2carpros.com/articles/idle-air-control-valve-service
https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

This may or may not trigger the check engine light.
If your check engine light is illuminated, you will need to get it scanned first, as it can help with the diagnosis.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing
I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.

Images (Click to enlarge)

Professional Diagram for 2CarPros Members
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Sep 5, 2021 at 9:30 PM