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Q: High idling happening occasionally after driving over 8 miles

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My car sometimes idles high. It happens suddenly and last usually until I restart the car. Then, several weeks could pass without any issue only to randomly appear again. The mileage is 150,000. When it happens, the car would go very fast without the acceleration on my part. The same thing is with reversing. It would go so fast that I would have to apply brakes. The engine would get noisy as I stop the car in park. This accelerating occurs usually after the car is in motion for over eight miles. Also, there is no check engine light. I took the car to the shop and they couldn't find anything wrong. The issue still occurs occasionally. What should I do?

Hi there. Most of the time this is caused by a problem with the throttle body. I usually clean it out first and inspect it for wear. If there is wear around the throttle plate then it needs to be replaced. If not the cleaning may take care of it. If it doesn’t then I test the idle control valve and the throttle position sensor as both of these will cause this. If those are also fine then it may be a sticking EGR valve but that is not as common. If you want to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to inspect your high engine idle.

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