I have a 2002 trailblazer with 115k miles.one day the car started running really rough at low idle and shakes bad,seems to run smoothly at higher revs...wondering what it could be
Hey there. This may be related to 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 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. This is all controlled by the idle air control valve. This can also be caused by other things as well such as low fuel pressure or dirty or leaking fuel injectors causing an over fueling situation. I would recommend having an expert from YourMechanic come to your location to verify the cause of the rough idle and replace the idle control valve if faulty.
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