Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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