Drop In Idle Speed

INPUT SIGNAL FROM THE AUTOMATIC TRANSMISSION





Fault Symptom.
Engine idling speed drops when the selector lever is moved away from P or N.

Conditions.
No diagnostic trouble codes.





Diagnostic Procedure.
1 Check DRIVE performance

- Connect an ISAT scan tool.
- Turn the ignition switch to the ON position.
- Select "READ ON/OFF".
- Select "DRIVE".
- Check whether an input signal is present by moving the selector lever from P and N to another gear position.

Is the ISAT scan tool reading correct?

YES
^ Change the idle air control valve. Continue with point 3.
NO
^ Continue with point 2.





2 Check the DRIVE signal

- Remove the Motronic control module.
- Connect a test lamp to the Motronic control module's connector between:
^ pins 86 and 34.
- Turn the ignition switch to the ON position.
The test lamp should light up when the selector lever is in any position except P and N.

Test results OK?

YES
^ Continue with point 3.
NO
^ Check and if necessary repair or replace the lead between pin 86 of the Motronic control module and pin 11 of the TCM control module.

If the lead is OK, continue fault diagnosis in the Automatic Transmission.




3 Final check

- Check whether the DRIVE fault symptom persists.

Does the trouble persist?

YES
^ Continue at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO
^ The steps taken to rectify the fault were correct.