Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idling speed is controlled via a single-coil idle air control (IAC) valve on the basis of a PWM voltage from the electronic control module.

Automatic idle speed control is adaptive, i.e. it adapts continuously to changes that take place during the life of the engine. These changes may be wear in the engine, dirt or leaks in the intake manifold or throttle body.

The engine control module is programmed to maintain idling speed constant at 850±50 rpm when the engine is warmed up at the same time as the throttle position sensor indicates idle speed.
Engine speed compensation takes place when A/C is switched on and when a gear position other than P or N is selected on cars with automatic transmission.





When the accelerator pedal is not activated and the throttle is closed, the engine receives air only via the idle air control valve.

The ECM controls the degree of opening in the valve to keep idling speed constant. This means for example that the valve opens slightly more when the A/C compressor is switched on or if DRIVE has been selected, in order to compensate the idling speed, which would otherwise fall.

The idle air control valve, which has a single coil, is supplied with current from the main relay. The valve is controlled by a 500 Hz PWM signal from pin 49 of the control module. The longer the control module keeps pin 49 grounded, the wider the valve opens.

The control module is programmed to maintain engine idling speed at 850 ± 50 rpm. Rapid changes in idling speed cannot be compensated for by changing the flow of air. Instead, ignition timing at idling speed is so arranged that engine speed is maintained at a constant level.

If there is an open circuit to the idle air control valve, the opening in the valve is set by a spring so that the idling speed is at least 1000 rpm when the engine is warmed up.