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Q: idle is high after driving

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i am stumped as to why my 92 ford explorer idles very high after driving it. upon startup, it will idle around 500-700 rpm. after i drive it for any fair amount of time (5 miles or more), i will shift into park and the idle goes up to around 1000-1200 rpm. just did an oil change recently, brand new spark plugs, checked pcv valve (still good). no vacuum leaks. what could be the issue?

My car has 243000 miles.
My car has an automatic transmission.

Hey there. Normally a vacuum leak is the most common cause of a high idle but many issues may cause this. Other possible causes of a high idle are improper sensor inputs, an idle air control valve, a faulty engine coolant temperature sensor, a stuck throttle body, a throttle body cable stuck, a bad power steering pressure sensor, AC high pressure sensor or a problem with the ECT (electric control transmission).

As you can see, many different systems cause a high idle condition. With the high idle not occurring until after the vehicle has been heated up, it appears there may be a heat related fault such a sensor reading improperly once it gets hot, or an intermittent issue with the IAC sticking sometimes. A complete inspection will be the easiest way to diagnose your high engine idle.

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