When the STA signal to the ECU is on, the ECU cycles the VSV at a 100% duty cycle to improve startability. The ACV does not have any effect on cold fast idle or warm-up fast idle speed.
When the engine has reached normal operating temperature, and the IDL contact is closed, the ECU uses a feedback idle speed control strategy to control warm curb idle speed. When loads are applied to the engine from the automatic transmission or electrical devices, the ECU adjusts target idle speeds accordingly. When the IDL contact is open or any time the Air Conditioning (A/C) signal to the ECU is on, the ECU maintains a constant duty cycle ratio to the ACV, allowing a fixed amount of by-pass air to flow.
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