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 oil temperature of approx. 16°C (61 °F), the idle speed is regulated to 800-950 rpm with the transmission in PARK or NEUTRAL, 650-750 rpm with the transmission in DRIVE or REVERSE. With oil temperature above approx. 16°C (61 °F), the idle speed is reduced to 600-700 rpm with the transmission in PARK or NEUTRAL, 450-550 rpm with the transmission in DRIVE or REVERSE.

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 is taken from the oil 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.
- At idle (without additional consumers) the idle speed adjuster operates with currents higher than 400 mA.
Four idle speeds will result depending on operating conditions and engine oil temperature.

IDLE SPEED AND PARTIAL LOAD IDENTIFICATION
With the throttle valve slightly opened, the idle speed adjuster is provided with a speed of approx. 850 rpm via the throttle valve switch and control unit. When the throttle valve is closed quickly, the engine speed cannot drop below 450 rpm.

When 850 rpm is exceeded, the current increases proportionally with the speed up to approx. 1000 rpm. Above that number the air flow rate is constant.

IDLE SPEED STABILIZATION WITH REFRIGERANT COMPRESSOR ACTIVATED
(At Normal Operating Temperature)
A delay valve has been installed instead of altering the contact relay for activating the magnetic clutch of refrigerant compressor. This activates the control unit prior to activating the refrigerant compressor. Prior to the increased engine load caused by including the refrigerant compressor, the idle speed adjuster opens to the extent that the engine continues running smoothly.

IDLE SPEED LOWERING WHEN ENGAGING A DRIVE POSITION
(At Normal Operating Temperature)
The starter lockout switch is closed in selector lever position "P" or "N" which grounds terminal 8 of control unit via coil of starter solenoid switch.

With driving position engaged, the starter lockout switch is opened and the ground connection is interrupted. The regulated speed changes from approx. 650 rpm to approx. 500 rpm.