2002 Chevrolet Impala, 3.4L engine, Automatic.
Intermittent high idle upon start.
Intermittent high idle while driving (as if the cruise control is activated).
Intermittent high idle (audible) when at stop after driving (even if the car idled fine upon start).
Findings at Shop:
No diagnostic codes.
High idle blamed on IAC (idle control motor).
(It appears that when the car idle fine nothing is even sending questionable data to the PCM).
(It appears that when the car is idling high, nothing points to a specific sensor/control)
What I did:
Shotgun sensors until I found a something that seems to fix the problem.
IAC (intake air control valve, replaced at shop for $250.00 (parts and labor).
IAT (intake air temp sensor, purchased for parts store for $15.00).
TPS (throttle position sensor, purchased at stor for $40.00).
What finally worked for me was the replacement of the TPS.
The car now seems to be working fine (hopefully it continues to do so).
It could have been linked to all three for all I know.
I did replace them in steps (first the IAC, then the IAT, then the TPS).
The only thing that proved to make a difference was the new TPS.
My suggestion to anyone that has this problem.
Replace these three items, they are cheap when purchased at a parts store (not from the dealer).
They are all in the same area on the motor/intake.
All the parts should cost you less than $150.00.
You need some tools (torx drivers, extensions, socket wrench, etc).
For a novice, within one to two hours you should be done.
Hope it works for you.
I suffered with the problem for two years. I am so glad that it finally appears to be over!
Sunday, January 4th, 2009 AT 12:41 PM