CDI idle speed function

L07.16-0006-06

B4/6 Rail pressure sensor

B11/4 Coolant temperature sensor

B37 Pedal value sensor

CAN Databus

K1/7 Diesel engine management relay

L5 Crankshaft position sensor

N3/9 CR control module

N20 Air conditioning pushbutton control module

Y74 Pressure control valve

Y76 Injector

Function

In the idling speed range of the engine it is primarily the efficiency and the idling speed which determine the fuel consumption. A considerable portion of the fuel consumption is attributable to this operating state because of dense traffic. That is why a low idling speed is desirable, but it must not drop to such an extent in all operating states that the engine runs irregularly or even cuts out. In order to stabilize the specified idling speed, the control module varies the injected quantity until the measured actual speed is identical to the specified set speed. The set speed is influenced by the gear engaged and the coolant temperature.

The following signals are required for the idle speed control:

 Crankshaft position sensor L5

 Coolant temperature sensor B11/4

 Air conditioning pushbutton control module N20

 Pedal value sensor B37

 Rail pressure sensor B4/6

 Intake air temperature sensor B17

On vehicles fitted with automatic transmission engine speed after a cold start is controlled in line with the engine temperature.

Smooth running control

Because of mechanical tolerances and aging not all the cylinders of an engine produce the same torque. This results in "irregular" engine running particularly in the idle speed range. The control module now determines the variations in speed after each combustion and compares them with each other. The quantity of fuel injected for each cylinder is set in such a way on the basis of the speed differences that all the cylinders supply the same torque. If a vehicle speed signal is transmitted by the traction systems control module (N47), the smooth running control is deactivated.