Idle Speed Control

Idle Speed Control





General
Idle speed control is used to regulate the engine torque so that the balance between the torque developed by the engine and the torque required to keep the engine and its auxiliary equipment running is maintained.

The nominal idling speed of a warm engine is 650 rpm. The engine speed is higher just after starting, especially if the engine is cold. Nominal idling speed also depends on coolant temperature.

Idle speed control is active when the accelerator pedal is released and the vehicle speed is 0.

Torque control
The principle of idling control is that the engine works with a "torque reserve". Since ignition timing is retarded compared to that which would generate the best torque, engine torque can quickly increased by setting engine timing earlier. Slow changes are handled by throttle control.





With an idling speed exceeding the nominal, there will be an excess of engine torque and the idling function will then request a lower value until the nominal idling speed has been attained. When the idling speed is below the nominal value, there will be a torque deficiency and the idling speed will have to be increased to attain nominal idling speed.

ECM reads the value for the torque (Nm) necessary to keep engine speed at the requested value from its memory. This value is also an indication of the engine's internal friction and is used for correction during torque calculation.