Q: Engine idle fluctuates and dies.

asked by on December 12, 2016

I was driving down the road and my truck started to bog down and tried to die. I pulled over pop the hood and looked around everything seemed fine..I started it up and it was bogging down trying to die.. I waited awhile and it fixed itself.. So on the road I went 20 minutes later it did it again.. I can start it up but I have to keep my foot on the pedal if not it will die..
My car has an automatic transmission.

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This may be a couple of different things. Your truck has what is called a throttle position sensor. The throttle position sensor 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.

Your truck’s engine also has what is called an idle air control valve. 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. Since this valve is controlled by the vehicle’s computer, it will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your truck.

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