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Idle Speed: Description and Operation

Idle Control System Diagram
The idle speed of the engine is controlled by the idle air control (IAC) valve:
- After the engine starts, the A/C valve opens for a certain amount of time. The amount of air is increased to raise the idle speed.
- When the engine coolant temperature is low, the A/C valve is opened to obtain the proper fast idle speed. The amount of bypassed air is controlled in relation to engine coolant temperature.