Idle Speed Control
The ECM determines idle speed by controlling an idle speed actuator (dual winding rotary actuator) ZWD 5.
The basic functions of the idle speed control are:
- Control the initial air quantity (at air temperatures < 0C, the MDK is simultaneously opened)
- Variable preset idle based on load and inputs
- Monitor RPM feedback for each preset position
- Lower RPM range intake air flow (even while driving)
- Vacuum limitation
- Smooth out the transition from acceleration to deceleration
Idle speeds will vary (idle speed stabilization):
- During the warm up phase
- When a drive gear is selected
- At all electric fan speeds
- When airconditioning is activated
- When heating the passenger compartment
- If nominal RPM is modified (idle speed increase) by DIS service function (if applicable)
Emergency Operation of Idle Speed Actuator: If a fault is detected with the idle speed actuator, the ECM will initiate fail-safe measures depending on the effect of the fault (increased air flow or decreased air flow). If there is a fault in the idle speed actuator/circuit, the MDK will compensate to maintain idle speed. The EML lamp will be illuminated to inform the driver of a fault.
If the fault causes increased air flow (actuator failed open), VANOS and Knock Control are deactivated which noticeably reduces engine performance.