Idle Speed: Description and Operation

Idle Speed Control Siemens MS 41.1:

A dual winding idle speed control valve is used to maintain the idle speed on the MS41.1 system. The valve is the same design as used on the M50 TU engine. The valve is mounted under the intake manifold in the area of the throttle housing. The air inlet of the valve is connected to the air intake boot upstream of the throttle plate via a hose. The air outlet is ported directly into the underside of the intake manifold.

If the idle control valve or control circuitry is faulted, the valve mechanically returns to a predetermined bypass opening (21 % fail-safe) that allows the engine to maintain idle speed.

The control parameters of the idle speed control valve are the same as the DME M5.x system. The two valve windings oppose each other. By varying the duty cycle applied to the windings, the valve can be progressively opened, closed or held steady to maintain the idle at the specified speed.

The crankshaft position sensor, engine temperature sensor, air temperature sensor and air conditioning inputs are used to determine the position of the idle valve for stabilization.