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Q: when I stop at a red light, while car is still in drivebut not park and idling, rpms surge and sometimes car dies completely.

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whenever I pull up to a red light or stop sign, and hold my foot on the break waiting for it to turn green, rpms surge from 500 to 1000, and sometimes it dies completely, but if I put it in park the idle is fine, only whenver I put in drive and come to a stop on the road.

My car has 211000 miles.
My car has an automatic transmission.

A: Hi there. This unstable idle can be caused ...

Hi there. This unstable idle can be caused by a few things. If it is constant then I would check the throttle body first. If the throttle body is really dirty then this can happen. I will usually clean the throttle body first. If that does not help then I test the idle control valve as that will cause this if it is failing. If that is also fine then the engine more than likely has a vacuum leak. The engine will need to be inspected for a leak either visually or with a smoke test. Most of the time the vacuum leak is the result of a bad hose or a failing intake manifold gasket. If you need to have this unstable idle checked out, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose the idling issue.

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