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Q: Car bucks, jerks, and idles rough - 1991 Ford Mustang

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My car seems like it isn't getting any gas. I can press on the throttle and it stalls, i let off the throttle and it bucks and jerks like something is misfiring. I press it to the floor and it just chokes. It does idle rough also, it goes from high to low. I put new spark plugs in and it's still doing the same thing.

My car has 240000 miles.
My car has an automatic transmission.

A: Hey there. This may be a sign of a failing ...

Hey there. 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 and 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 750-800 RPM (for most cars), this may indicate a dirty or faulty idle air control valve. In cases where this valve is clogged 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 qualified professional from YourMechanic can come to your location to replace the idle control valve for you.

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