Q: Won't hold idle - 1999 Ford F-150

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I tried to start it and got a backfire from under the hood, but it did not start. I turned the key again and it started, but it revs to 3000 rpm, and then tries to drop to stall unless I work the gas peddle. It gives of a thin white smoke from the rear of the motor when I force it to stay running for a minute, and whistles from what sounds like somewhere in the front or passenger side of the motor. I don't see any vacuum hoses loose. What is my truck's problem?

My car has 247000 miles.
My car has an automatic transmission.

Hey there. This may be a sign of a dirty or failing idle air control valve or potentially an intake air leak. The idle air control valve monitors the air intake as it is mixed with fuel as it gets injected into the motor.

When this is not working correctly, this will cause an unbalanced load of air and fuel into the motor causing the erratic idle as you have experienced. An intake air leak may also cause this kind of idle surging as it creates a similar imbalance of air/fuel to be supplied to the motor.

The whistling sound may also be an indication of an intake air leak or potentially a vacuum leak.

If you would like to have this checked out, have a certified professional diagnose the idling issue and follow through with proper repairs.

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