Idle Speed Stepper Motor
Idle speed control (also called idle air control) provides a stable idle speed which remains almost constant under all temperature conditions, even when supplying electric consumers at idle speed, or when subjected to age-related changes to the engine.
The control unit controls the idle speed using an idle speed stepper motor.
It regulates the amount of air required for maintaining the idle speed according to load condition and coolant temperature. If this engine speed deviates from the nominal engine speed, coil 1 or coil 2 of the stepper motor is actuated by opening or closing the tapered valve.
The tapered valve aperture is proportional to the number of steps in the stepper motor.
The control unit can actuate the motor in 256 single steps 1). The current position of the stepper motor can be read out from the control unit data stream using TECH 1 and the latest program module. This sensitivity guarantees a maximum 25 rpm idle speed deviation from the nominal value.
1) In normal operation, the control unit only uses 160 steps. The remainder are required when
the control unit resets (IAC reset) for finding the reference position.
Idle Speed Stepper Motor (continued)
The idle speed stepper motor or idle air control has therefore the following tasks:
- To keep a constant idle speed with the engine at operating temperature under all loads.
To regulate the warm-up function.
1 Valve taper
2 Front bearing
3 Rear bearing
4 O-ring
5 Threaded spindle
6 Plug
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