Idle Up Control Valve: 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 engine 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 may be wear in the engine, dirt or leaks in the intake manifold or throttle body.

The control module is programmed to maintain a constant idling speed of 900 ± 50 rpm when the engine is warmed up at the same time as the throttle position sensor indicates idling position.

Engine speed is compensated when AC is switched on and when a gear position other than P or N is selected on cars with automatic transmission.

The idling speed for the engine must be 90O ± 5O rpm.





When the accelerator pedal is not activated and the throttle plate is closed, the engine only receives air via the [1][2]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 AC compressor is switched on or if DRIVE has been selected, in order to compensate the idling speed, which would otherwise fall.

The [1][2]idle air control valve, which is single-coil, is supplied from the main relay. The valve is controlled from pin 49 on the ECM with a 500 Hz PWM. The valve opens more the longer the ECM keeps pin 49 grounded.

The ECM is programmed to keep the engine idling speed at 900 ± 50 rpm. Rapid changes in idling speed cannot be compensated for with a change in air flow. Ignition control in idling is instead designed so that engine speed is kept constant.

If there is an open circuit to the [1][2]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.