My 2005 pontiac grand prix will start normally but then it will start to sputter. The rpms will drop to 500 and will try to die unless I give it gas. Its goes away after about 25 seconds but still has driving issues. No check engine light. The light came on and said heater fault in upstream o2 sensor but went off.
Try a throttle body cleaning first before throwing parts at it.
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That was the first thing I did. Ive had a low idle problem for a while but this is a recent symptom. I gave it a tune up a year ago. Any other advice would be appreciated.
Did you find out what it was?
20 seconds is about how long it takes for O2 sensors to start working. It could have been low fuel pressure, or a vacuum leak.