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
  Fig 1: Identifying Idle Speed Control Operation

  Courtesy of BMW OF NORTH AMERICA, INC.

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.