The idle speed actuator is a bypass air valve. The idle speed actuator shown as an example consists of a closed cast housing with flange-mounted solenoid valve servo unit. Attached to this is a nozzle holder, which releases different air cross sections by moving the servo unit, and can therefore control the air mass flow when the throttle valve is closed.
The idle speed actuator is responsible for regulating the engine speed as part of the overall idle-speed control of the engine management system. If there is a sudden change to the engine load condition when in idle mode (e.g. air-conditioning system being switched on, creep speed in 1st gear, or activation of another electrical consumer), air and fuel are also required in order to prevent the engine from stopping. If the engine speed falls below a certain critical value, which is stored as a constant in the control unit memory, the solenoid valve is activated and an increased air flow rate is achieved. The opening time of the injection valves is simultaneously extended and adapted to the engine's requirements.