Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control Valve





Description

On 1986 and later cars the auxiliary air valve is replaced by an idle air control valve (IAC) which also compensates for momentary load increases at idling speed.

The idle air control valve is bolted to a bracket mounted on the intake manifold. The valve allows a controlled flow of air to bypass the throttle butterfly. The volume of the air is determined by the degree of opening of the idle air control valve.

The idle air control valve consists of a slide valve with a reversible motor. The motor has two windings and maintains a continuous reciprocating action, turning the slide through a maximum angle of 900. The motor receives signals from the control module.

Due to the motor's continuous, limited-travel reciprocating action (noticeable only as vibration), the opening of the valve can be varied within extremely short periods of time (opening/closing in about 150- 200 ms). This permits the air flowing through the valve to be controlled at all times so that the volume necessary for obtaining the desired constant or increased idle speed can be achieved as required.

On model year 1989 and later cars the earlier dashpot function has been discontinued. This function is now programmed in the control module.

The dashpot is a mechanical throttle damper which delays closing of the throttle when the accelerator is released and helps to prevent the exhaust gases from having an unfavorable composition. Greater comfort during engine braking is also provided by the dashpot.