The optimum value stored in the ECM is determined by taking into consideration various engine conditions, such as during warm-up, deceleration, and engine load (air conditioner, power steering, and cooling fan operation). The target engine speed is the lowest speed at which the engine can operate steadily. The ECM then controls the step position of the IACV-AAC valve so that engine speed coincides with the target value memorized in ECM. The crankshaft position sensor (POS) detects the actual engine speed and sends a signal to the ECM. when the step advances, the opening is enlarged.) The opening of the valve is varied to allow for optimum control of the engine idling speed. One step of IACV-AAC valve movement causes the respective opening of the air bypass passage. This valve is actuated by a step motor built into the valve, which moves the valve in the axial direction in steps corresponding to the Engine Control Module ( ECM) output signals. The IACV-AAC valve changes the opening of the air bypass passage to control the amount of auxiliary air. Idle speed is controlled through fine adjustment of the amount of air that bypasses the throttle valve via Idle Air Control Valve IACV) and Auxiliary Air Control AAC) Valve. This system automatically controls engine idle speed to a specified level.
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