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Other air request

Other air request





Idle speed control

When the accelerator pedal is fully released and the vehicle speed is zero the system regulates the air mass/combustion that is required for the current idle speed to correspond with the requested. The air requirement is stored in the control module memory (adaptation). The requested idling speed is stored in a table in the control module memory and is dependent on the coolant temperature. At -30 °C the value is 1200 rpm and as the engine gradually warms up it, the requested engine speed drops to 825 rpm.

TCM sends bus information "Selector lever position”, unit P, R, N, D, 3, 2 or 1. The value is used by Trionic T7.

When any value other than P or N is selected, the requested air mass/combustion is increased to compensate for the impending increase in load. This is to fully compensate for the increased engine torque requirement of the automatic transmission so that a rapid decrease of the idling speed is avoided before the idle speed control has time to compensate. The air requirement in any other position than P or N is stored in the control module memory (adaptation).



As soon as the car is in motion, the idle speed control is disengaged and the engine receives the adapted air quantity.

Diagnostics


• If the idling speed is too high, diagnostic trouble code P0507 will be generated.

If the idling speed is too low, diagnostic trouble code P0506 will be generated.

• The difference between the requested idling speed and the current idling speed can be read with the diagnostic tool, as can whether idle speed control is active.