An idle actuator in the form of a valve is fitted in the S54 engine. The component is located below the intake bridge. There are three electrical lines, of which the lines T_LLFS5 (control: ”valve open”) and T_LLFS0 (control ”valve closed”) handle the control and line U_HR<2 handles the supply. If the function is unimpaired, a signal on the control lines opens or closes the valve. Manual manipulation of the valve is prohibited.
The idle speed actuator is now responsible for several tasks and is therefore an important component in the intake air tract of the engine.
Small air leaks which may occur, for example, at leaking gaiters/cylinders or in the event of a varying gap in the throttle valve can be compensated up to a certain extent by the idle speed control valve.
The idle speed control valve opens a little more during the engine coasting phase and closes just before reaching idle speed. This prevents a high intake pipe vacuum and blue smoke emission (oil vapour via valve stem seals).
During engine start, the idle speed control valve enables an opening cross section that is above that of idle speed. This ensures the engine starts more efficiently.
The throttle valves are only activated at higher speeds, freeing up a considerably larger flow cross section for fresh air intake into the six cylinders.
So that there an adequate vacuum can be set up for the brake booster in motor sports engines even at low engine speeds (i.e. throttle valves mainly closed), there is a separate suction-jet pump (see corresponding functional description).
The idle speed control valve features an emergency operation opening gap which ensures certain emergency running functions in the event of power failure.