Idle Maintenance Systems

On all except EML equipped engines, idle air is regulated through the idle control valve to maintain engine idle under all conditions. EML equipped engines (M73 and M70 V12s) do not have idle control valves. The EML system provides the idle function.







Two Wire Idle Control Valve: The idle control valve of the M1.7/ M42 engine is a two wire control valve. The idle control valve is spring loaded closed. It will failsafe to a fixed opening to allow the engine to idle in the event of a power failure. One lead of the valve is powered, and the valve's opening is controlled by a modulated signal on the ground lead which opens the valve against spring pressure.

Three Wire Idle Control Valve: All other systems use a dual winding (3 wire) idle speed control valve to maintain the idle speed. If the idle control valve or control circuitry is faulted, the valve mechanically returns to a predetermined bypass opening (21% failsafe) that allows the engine to maintain idle speed.

This valve has two valve windings which 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 idle speed control valve is used as part of the ASC+T system during MSR regulation to reduce the engine's braking effect during decel.