Idling speed ignition timing
When idle speed control is active, the ignition advance is 10° before top dead center (BTDC).
Depending on the coolant temperature, the idle speed control requests an idling speed.
If the current engine speed falls below the requested speed, e.g. when the power steering pump loads the engine as the steering wheel is turned, the ignition is advanced by up to 10 °.
The aim is to increase engine torque quickly to compensate for the drop in engine speed. The extent of the ignition advance depends on the difference between the actual and the requested engine speed. Similarly, the ignition will be retarded if the actual engine speed is higher than that requested.
The regular idle speed control that acts on the throttle valve, and hence regulates the quantity of air mass/combustion, works more slowly than the idle speed control using the ignition timing.