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Q: engine is shaking - 2006 BMW 325i

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engine is shaking from time to time , with RPM up and down with less power for the car when its shaking. i replaced the coils and the spark plugs with no success , what should be the issue ? , i think it's an air issue...what you think ?

My car has 135000 miles.
My car has an automatic transmission.

A: Hello. This may be a sign of a failing idle...

Hello. This may be a sign of a failing idle air control valve. The idle air control valve is located on or near your intake manifold that monitors the air intake as it is mixed with fuel prior to being injected into the engine. 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. However, when the engine RPM drops below the normal range of 800 RPM (for most cars), it is more than likely that you are dealing with an IAC valve problem. In cases where this valve is clogged or is failing, your vehicle will stall instead of slowing to an idle after the release of the throttle. A certified professional from YourMechanic can come to your location to diagnose the shaking issue and proceed with proper repairs.

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