High and low Idle

2001 PONTIAC AZTEK
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PFARROYO
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Six cylinder all wheel drive automatic 90,000 miles.

My vehicles engine is starting to idle high, sometimes, and to idle low, sometimes. Sometimes while driving the engine will accelerate without gas and upon putting in park the rpm's will rise to 3500-4000. Sometime while driving the idle will be low, 400 rpm's at stop and sometimes stall. Had mechanics look at problem but no advice. Had fuel filter changed, seemed to work for a couple weeks, but the problem still persists. Tried oil treatment, gas treatment and higher octane fuel. Any Ideas/Solutions?
Nov 5, 2010 at 3:17 AM
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WRENCHTECH
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The first thing you want to do is check thoroughly for any vacuum leaks in the engine as this will cause that symptom. If all vacuum leaks are eliminated, you may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carburetor cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.
Nov 5, 2010 at 7:11 AM