What Are the Functions of an Idle Control Valve?

The idle control valve controls engine idle speed.

Engine idling refers to the speed at which an internal combustion engine runs when the gear is disengaged. This idle speed is controlled by a device called an idle control valve, or idle air control valve.

Function

Idle air control valves monitor and adjust the air that flows through the throttle plate in order to maintain specific engine RPM, or revolutions per minute. The idle air control valve is controlled by the engine ECM, or electronic control module, which transmits electronic signals to the valve to make changes to engine idle speed.

Increasing RPM

The idle air control valve contains a pintle which is a shaft with a cone-shaped point. As the pintle pulls out, the tip shifts to the valve opening to block some or all of the air flowing through the throttle. This causes the amount of surrounding air around the throttle plate to increase, which in turn increase the engine RPM at idle.

Decreasing RPM

The pintle also retracts in response to signals from the ECM. When the pintle shifts away from the valve opening, it decreases the amount of air around the throttle plate, thereby decreasing engine idle speed.

References

• 2CarPros: How Idle Air Control Valve Works
• "Car Science"; Richard Hammond; 2008

Resources

• "How to Repair Your Car"; Paul Brand; 2006