Fluctuating Idle problems

1991 BUICK SKYLARK

100,000 MILES • 2.5L • 4 CYL • 4WD • AUTOMATIC

SNEDWARDS39

MEMBER
7 POSTS

Car either idles too high or too low already replaced the throttle positioning sensor and the idle control valve. checked for vacuum leaks couldn't find any. did a complete tune up. I'm not car smart at all and nobody can seem to fix the problem I am having.

Jun 29, 2021 at 6:07 AM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

Good morning,

I would disconnect the idle air control motor and see if the fluctuation stops. The ECM may be commanding the air control pindle in and out causing this issue. The ECM does this based on the input from the O2 sensor.

https://www.2carpros.com/articles/engine-idles-too-high

If the motor stops hunting, then you may have a bad ECM. That is what controls the motor.

I attached the procedure for the ECM below for you.

Roy

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