Q: I have a 2008 Acura TL. At idle the car is revving to low at about 500-600 rpm. The check engine light is also on.

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My car idles too low at 500-600 rpm. When the car is put into gear the car bumps up 100 rpm(between 600-700). The check engine light is on all the time and the car shakes at idle but smoothes out at higher rpm(850 and on). This only occurred after I ran the car a bit hard on some twistier roads. The car also has trouble turning over on start up and struggles to get up to 500 rpm.(the car hasn't failed to start yet). The engine pulses evenly.

My car has 150000 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 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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