Q: Intermittent rough idle

asked by on December 11, 2016

My Nissan idles rough for 5-10 seconds then smooths out for 10-15 seconds before idling rough again, repeating the cycle. This happens whether the engine is hot or cold. If the engine is cold and it is less than 40 degrees Fahrenheit outside, the car will stall a few seconds after idling rough. On random days (maybe 4-5 day per month), instead of idling low, it idles between 1500-2000 RPM. Driving down the highway, occasionally it feels like it has no power and will not accelerate like it should. Again, happens for a few seconds then it's back to normal. There is no check engine light. The car does this no matter if it's in park, neutral, or drive.

My car has 238000 miles.
My car has an automatic transmission.

This may be a result of a dirty or failing 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. 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 replace your idle air control valve.

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