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Q: engine revs up and down when in park

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engine revs up and down when in park and when driving

My car has 130170 miles.
My car has an automatic transmission.

A: The idle is controlled by the idle air cont...

The idle is controlled by the idle air control valve and if it cannot keep the engine idling it will keep trying to rev the engine up to compensate. A vacuum leak, sensor that has failed, or an EGR system malfunction could potentially be the cause of the erratic engine you're experiencing.

A mechanic will be able to diagnose the rough idle for you and quote the needed repairs. For this vehicle, the engines are very sensitive to vacuum leaks in the intake air tube, between the mass air flow sensor and the throttle body. If the tube is cracked it will need to be replaced before anything else to see if the idle settles down.

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