Idle became erratic and engines shuts off and on at speed. Problem is intermittent and does not show check engine light
My car has an automatic transmission.
As you know, 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. When the engine RPM drops below the normal range of 750-800 RPM (for most cars), this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. Depending on the severity of how dirty the valve may be (in your case, maybe not enough to register the check engine light), this may be intermittent or erratic. Although normally the idle air control valve monitors air intake at low or idle speeds, this may affect the the functionality of it in the case of driving down the highway and quickly letting off the gas pedal. As you know, part of the job of the idle air control valve is to slowly bring the engine down to an idle or low speed when reducing engine RPM's. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your idle air control valve.
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