IAC Valve

IAC Valve

An idle control valve does exactly what its name indicates, controlling the idle speed of the engine and preventing it from stalling. Its failure may cause a variety of problems, including incorrect engine operation and poor fuel efficiency.

Abnormal idle speed

Your idle air control (IAC) valve is almost never fully closed or open. If it sticks in its closed position, your engine may stall or be close to that. On the other hand, the alternative position of the IAC valve will make the engine run too fast even if your vehicle is not moving. Besides, a faulty IAC valve may cause engine surging, when its speed occasionally goes up and down.

Your engine stalls

An improperly operated idle control valve may cause the engine to suffer from a lack of air, which is why it can stall.

The check engine light turns on

Your engine control unit monitors the operation of the IAC valve. If any problem appears, the ECU will alert you of the trouble.

You can’t start the engine

If your IAC allows too much or too little air entering the combustion chamber, the engine won’t start. 

What is the function of an idle air control valve?

The job of your IAC valve is to control the engine’s idle speed by increasing or reducing the volume of air that goes around the throttle plate. It is usually attached to the throttle body for ease of operation.

Your engine control unit relies on your coolant temperature sensor and throttle position sensor to determine when and how much to open or close the IAC valve. Based on the received data, it sends needed voltage to the valve’s motor that moves its mechanism.

On newer vehicles, the function of an IAC valve is performed by an electronic throttle actuator.

Should I replace my faulty IAC valve?

Some symptoms that you may recognize as signs of a bad IAC valve can be caused by other engine parts. You should ask your mechanic to test the valve before its replacement.

In some cases, simple cleaning of the IAC valve’s passages or checking and fixing its circuit may prevent you from purchasing a new idle air control valve. If nothing helps, replace the IAC valve with a brand-new one. Installing a used valve is not a good option since it may be clogged with carbon or worn-out.