[Porsche944]

The idle stabilizer is a motor operated "throttle valve" that takes the place of the Auxiliary Air Valve and the A/C supplementary air solenoid.

On the early cars the AAR is used as part of idle and mixture control during warm-up. When the engine is first started the AAR is fully open to allow additional air to flow into the intake tract. The AAR uses a bi-metallic (temperature sensitive) device to control how far the valve is open. As the engine comes up to temperature the AAR closes. When the AAR is fully closed engine idle is controller by the idle by-pass on the throttle body. When the A/C is running the A/C solenoid opens and allows additional air to flow into the intake to compensate for the additional mechanical load.

On the later cars the AAR and A/C solenoid were replaced by the Idle Stabilizer. This device is controlled by the DME. When the DME sees a change in RPM (at idle) a signal is sent from the DME to the IS.