Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Valve:

Sent by the fuel injection ECU:
The idle air valve (located below the throttle body) provides the control for constant idle speed. In order to set the correct air valve opening to achieve constant idle speed, the fuel injection control unit uses information from the air mass meter, A/C switch, throttle valve switch and the ignition control unit (RPM signal) to regulate the output current to the idle air valve. This means that the idle valve is not affected by air leaks or a jammed throttle valve.

Idle Air Valve Operation:

When the current is off, a spring sets the idle valve opening for an idle speed of 1050 ±50 RPM. Once the engine is running, the fuel injection control unit ensures that the idle valve is more or less open at all engine speeds to prevent the development of unnecessarily high vacuum in the intake manifold during sudden deceleration.

OPERATION
When the throttle valve switch idle contacts are closed during idling, the fuel injection control unit will send a current to the idle air valve electric motor to keep the idle speed at the correct level. This speed is preset in the fuel injection ECU and should remain constant disregarding engine load or conditions.
If the throttle valve switch idle contacts are open (engine above idle speed), the fuel injection ECU will not send a current. The idle air valve will close to its default position, thus staying partially open so the vacuum in the intake manifold is reduced when the throttle valve suddenly closes.