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Q: Rough idle and sputters while driving

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my suburban runs great cold for about 10 mins and it slowly drops rpm and and then soon after it reaches 500rpm engine light comes on and it runs rough. i've replaced plugs, wires, fuel filter. and a lot of others. it does it every time its not like a once in a awhile its every time. and driving it sputters about stalls but doesn't.

My car has 179000 miles.
My car has an automatic transmission.

A: Hey there. This is a common sign of a faili...

Hey there. This is a common sign of a failing idle air control valve. The idle air control valve 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. As you let off the gas, the RPM slowly returns to the normal idling speed. This is all done by the idle air control valve. When the engine RPM drops below the normal range of 750-800 RPM (for most cars), this may indicate a dirty or faulty idle air control valve. In cases where this valve is dirty or failing, your vehicle will stall instead of slowing to an idle after the release of the throttle. If you would like to have this taken care of, a certified professional, like one from YourMechanic, can come to your car's location to replace the idle control valve.

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