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The Idle Speed Controller Valve, or otherwise known as the Idle Air Bypass System, is responsible for maintaining a smooth, and consistent idle, under different Engine Loads, and temperatures.
It does this by allowing a certain amount of air, to bypass the Throttle Body Butterfly, thereby increasing the amount of air entering the engine, under certain conditions, thereby increasing Engine RPM.
have a look at
and go down to idle speed controller, my car used 2 idle rough untill i done this now its fine.
hope this helps yas