Idle Speed: Description and Operation

Idle Control System

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. Refer to the system diagram to see the functional layout of the system.

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.




Idle Control System Diagram

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 controlled in relation to engine coolant temperature.