Idle Control System

Idle Control System




The idle speed of the engine is controlled by the Idle Air Control (IAC) valve:

- After the engine starts, the IAC 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 IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is thus controlled in relation to engine coolant temperature.

When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is pressed, the P/S load is high, or the alternator is charging, the ECM controls current to the IAC valve to maintain the correct idle speed.

Brake Pedal Position Switch
The brake pedal position switch signals the ECM when the brake pedal is pressed.

Electrical Power Steering (EPS) Signal
The EPS signals the ECM when the power steering load is high.

Engine Start Switch
The engine start switch signals the ECM when the engine is cranking.




Idle Air Control (IAC) Valve
To maintain the proper idle speed, the IAC valve changes the amount of air bypassing the throttle body in response to an electrical signal from the ECM.