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Q: My car will not idle at a stop light.

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my car shuts off sometimes but it will start back up but it would not hold an idle I have to hold down the Gas Pedal in order for it to catch idle
My car has an automatic transmission.

A: This may be a sign of a failing throttle po...

This may be a sign of a failing throttle position sensor or a failing or dirty idle air control valve. The throttle position sensor (TPS) is a sensor used to monitor the throttle position of the throttle plate inside the throttle body in relation to your foot position on the gas pedal. Based upon the inputs from the sensor reading your foot's position on the pedal, the ECU then makes the direction to supply more or less fuel to the motor. When this sensor is not working properly, this can cause intermittent responses when pressing the gas pedal.

The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. 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.

I would suggest having a professional from Your Mechanic come to your location to diagnose your idle air control valve and throttle position sensor.

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