What Is Idle Air Control?

Engines require three things to run: air, fuel and spark. Though the main throttle butterfly controls the majority of the engine's airflow, all engines must include a provision to feed the engine while the throttle is closed at idle.

Carbureted Engines

The carbureted engine's solution to idle air control is usually to adjust the main valves so that they always hang open just a bit, ensuring the engine is never starved of air.

Bleed Valves

Those carbureted or throttle-body injected engines that do not use the system previously described employ separate air channels cast into the throttle bores or carb body to regulate idle airflow.

Electronic IAC

Modern fuel-injected engines use an electronically controlled IAC (Idle Air Control) valve to regulate airflow.

IAC Function

Electronic IAC systems allow the computer to make minute adjustments for air pressure, air temperature, fuel quality and engine temperature to ensure optimum engine efficiency.

Cat Light-Off

Catalytic converters require a certain amount of heat to function. As such, the IAC serves the dual function of keeping the engine running and adjusting the air-fuel ratio to expedite cat light-off.

References

• AutoEducation.com
• FordPower Forum
• MuscularMustangs Forum

Resources

• Cleaning an IAC Valve (Video)