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Q: Idle sounds real rough

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when I crank my truck up it sounds rough sometimes because I think it I wanted to know if I need a coil or cap and rotor. also sometimes when I crank it up it cuts right off and when I crank it up I have to accelerate the gas to keep it from cutting off

My car has 250000 miles.
My car has an automatic transmission.

A: This may be a sign of a failing idle air co...

This may be a sign of a failing idle air control valve. The idle air control valve is located on or near your intake manifold that monitors the air intake as it is mixed with fuel prior to being injected into the engine. This valve 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 slowly returns to the normal idling speed. However, when the engine RPM drops below the normal range of 800 RPM (for most cars), it is more than likely that you are dealing with an IAC valve problem. In cases where this valve is clogged or is failing, your vehicle will stall instead of slowing to an idle after the release of the throttle. If you would like to have this checked, a qualified pro from YourMechanic can come to your car's location to diagnose the rough idle and proceed with the right repairs.

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