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Q: Low idle and stops, sometimes stalls at idle.

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Low RPMS @ stops/idle (rpms under 650), stalled @ a red light (rpms were under 500), extremely low rpms driving fast (speeds around 40-50/rpms under 1600), & sounds ruff driving (sounds like its working very hard, it sounds like the engine is "whinning"). Trans. was rebuilt 1 year ago & rechecked 40+ days ago. Oil change every 3000- 4000 miles. Throttle body & Idle control valve are clean. No codes have shown. Ideas on what could be wrong etc?

My car has 190000 miles.
My car has an automatic transmission.

A: As you know, the idle air control valve rea...

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. As 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. 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. You can test the functionality of the valve by checking its electrical resistance if you have access to an ohm meter. To do this, disconnect the IAC valve, connect an ohmmeter to pins 2 and 3 of the valve. If you get a resistance value between 10-14 ohms, it indicates IAC valve is working as it should. Next, connect the ohmmeter to pins 1 and 2. If you do not get a resistance value between 10-14 ohms, the IAC valve may need to be replaced. 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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