Q: Q: Problem with RPM

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I had a new air filter installed 09/03/2017, the next day after driving for about 2 hours on the interstate using cruise control, after turning the cruise control off and going a speed of 30 - 45 mph the RPM on the car would begin to increase and then surge up really quickly and drop back down as if the car was trying to shift, however the speed would remain the same. This was also accompanied with a noise. The same person that installed the air filter, tried cleaning the mass air flow sensor and reinstalling the air filter. While test driving the car, when I put my foot down all the way on the gas the car wouldn't go, but eventually would gain a little speed. He did something else(not sure) and that issue stopped. So while I was driving home the car began to hesitate and stop. I had a few different people all say something different is wrong: Throttle Position Sensor, Idle Air Control Valve, leaky hose, Mass Air Flow Sensor and transmission.

My car has 81000 miles.
My car has an automatic transmission.

What you are describing sounds like a dirty or failing idle air control valve. The idle air control valve monitors 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 and 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 while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about 750-800 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 vehicle.

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