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Q: What is the problem? No one can tell me

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New fuel filter and new fuel pump. Idles great in park with no A C on. Begins to idle rough when put in drive and real bad when A C is turned on.

My car has 92000 miles.
My car has an automatic transmission.

A: The vehicle idling in park with no A/C does...

The vehicle idling in park with no A/C does not really require much need for the idle air control valve. Once the vehicle is put in drive, this will put a load on the engine as the A/C will require an additional load.

The idle air control valve is supposed to compensate for the load and raise the idle up to compensate. If the valve is not working, or the throttle body and valve are dirty, then they may need to be cleaned or the valve may need to be replaced. Have the throttle body checked for excessive carbon deposits and cleaned as needed. Disconnect the idle air control valve when idling in park to see if engine stays running. If it does not, then you may have a vacuum leak or dirty throttle plates. To have these items tested, a certified technician from YourMechanic can come to your car’s location to diagnose the rough idling issue and let you know what needs to be done.

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