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Q: My engine idles heavy 1/3 of the time

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My car normally idles (when stopped at a light) at about 600 RPM. However, about one third of the time, it will rev up to 900 or 1,000 RPM and try to lurch forward. The check engine light does not come on when this happens. My car has 120,000 miles. What could be the cause?

A: If the throttle is sticking open or the idl...

If the throttle is sticking open or the idle air control valve is sticking open, would account for the check engine light not coming on. The vehicle would have to be checked to make sure the throttle is not being held open manually by the floor mat or by other means before looking at the idle air control valve to see if it is sticking. If the valve is stuck and you disconnected the electrical connector and it still does not lower then the valve is binding and would need to be replaced. This problem would need to be seen in person by a mechanic to diagnose it, and I recommend you have it looked at before it gets worse or causes more problems. If you need assistance with this, have a certified mechanic, such as one from YourMechanic, inspect your car's idling issue and make the necessary repairs for you.

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