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Q: Idle problem

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While in park and idling my truck will idle up and down it usually stays around 6-700 rpm, but at random times while idling It will jump up 5-600 rpm or so, What could cause this issue?

My car has 180000 miles.
My car has an automatic transmission.

Hello and thanks for writing in. What you are describing sounds like a dirty or failing idle air control valve. The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This is controlled by the vehicle’s computer which will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about 800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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