Idle Speed: Testing and Inspection

Check engine idle speed and exhaust contents (M40, M42, M43, M44) - vehicle with catalytic converter -







Requirements for all adjustments:
Engine at normal operating temperature (oil temperature > 60 °C).
Engine and ignition system functioning correctly.

Connect up or MoDiC.
Check idling speed:

1) Engine idle speed:
Check engine idle speed.


2) Exhaust test:
Insert exhaust sensor in exhaust tailpipe.
Check exhaust contents at idle speed.
Switch off exhaust extraction system for time of testing.
If nominal value is not achieved, exhaust contents can also be measured on each individual cylinder group.







If the exhaust idling speed values deviate from specified value:
Interrogate the error memory of the Digital Engine Electronics.
If the error memory on the oxygen sensor is set to closed-loop
Lambda control, continue troubleshooting with the oxygen - sensor tester 11 7 450.

Measure exhaust content in front of catalytic converter.
M42:
Disconnect plug-in connection to oxygen sensor and remove sensor.
Install special tool 1 0 094 in threaded neck of oxygen sensor.







M40, M43:
Unscrew bolts. Connect special tool 13 0 092 to exhaust manifold.
Connect measuring sensor of exhaust tester to special tool 13 0 092.
Check CO contents.
Switch off exhaust extraction system for time of testing.


3) NOTE:
Before correcting the exhaust/idle setting, first ensure that there is no malfunctions on the engine, in the ignition system or the fuel injection system.


For example, if the exhaust/idling speed value is too high:
- Check injector nozzles.
- Check fuel delivery pressure.
- Check coolant-temperature sensor.
- Check air intake system for leaks.
- Check idling speed valve.

For example, if the exhaust/idle value is too low:
- Check hoses and connections for idling speed control and localize the air leak.
- Check air intake system for leaks.
- Check idling speed valve