rpms go up and down when idleing on 2004 Pontiac Grand Prix

cars rpms go up and down when idleing. car has new cats and o2 sensors and check engine light is not showing anything is wrong?

by in Tempe, AZ on March 22, 2009
2 answers
ANSWER by on March 25, 2009
The cause of an idle surge can sometimes be hard to pinpoint. A sensor could be failing but not enough to turn the check engine light on. You may have a dirty throttle body or a fuel injector issue. This problem may need to be checked out by a qualified technician. If you don't have a regular shop that does your repairs check out the listings at www.repairpal.com.
ANSWER by on May 17, 2010
I had the same problem with my car start about 2 months ago and thought it was the O2 sensor as well, but it turns out it was the mass flow air sensor instead.
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