Idle Speed/Throttle Actuator - Electronic: Description and Operation

The idle speed adjuster is a lifting magnet with respective aperture which permits variation of air flow rate. The control unit provides the lifting magnet with a timed direct current in frequency range of approx. 200 Hz.

The air is picked up after the air flow sensor plate, but before the throttle valve. The respective air quantity will be combined with the respective fuel quantity via the air flow sensor plate.

Up to coolant temperature of approx. 42°C (108 °F), the idle speed is regulated to 750 rpm. With coolant temperature above approx. 42°C (108 °F), the idle speed is reduced to 500 rpm and kept constant.

When the ignition is switched on, the magnet is set to a fundamental frequency by way of electronic control system. The momentary engine speed is taken from the ignition impulses (Ignition Switching Unit terminal TD) and a signal is transmitted to the idle speed adjuster. The switchover point for the engine speed 750rpm or 500 rpm is taken from the coolant temperature switch.

Idle Speed Adjuster Open:

The idle speed adjuster has the following functions:

- With the ignition switch OFF, the aperture (1) is opened to maximum capacity.
- With the ignition switch ON (engine stopped), the idle speed adjuster is activated via electronic control system with approx. 1 ± 0.5 Volt (measured at idle speed adjuster with clutch plugged on). Aperture (1) is opened to maximum capacity.

Idle Speed Adjuster Closed:

- With the engine running, the idle speed adjuster operates continuously between 4 and 5 Volts, or 1050-1200 mA. The aperture is closed approx. 5 Volts. A slight air leak is permitted.
- At a speed above 900 rpm, the idle speed adjuster is activated with approx. 4.5 Volts, so that the aperture is partially open to prevent the engine from dieing in the event of a fast rpm drop.