Engine Speed Dips When Gear Is Engaged (Automatics)

ENGINE SPEED DIPS WHEN GEAR IS SELECTED (AUTOMATICS)

Conditions for Fault Tracing:
^ No DTCs present.
^ Engine hot.
^ Fault is permanent.

Fault Sources:
^ Open-circuit in signal lead from Transmission Control Module (TCM).
^ Signal lead short-circuited to ground or supply.
^ Contact resistance in connector.
^ Faulty gear selector mechanism or Idle Air Control (IAC) Valve.

TESTING PROCEDURE





Checking Signal From TCM
^ START engine and allow to idle.
^ Move gear selector lever to position N and note Scan Tool indication.





^ Compare indications with those in table in order to continue fault tracing.





Checking IAC Valve Connection
^ Clean and grease MFI Control Module and IAC Valve connectors.
^ Check if engine speed still drops.

If engine speed still drops:
- Try with new IAC Valve.





Checking Signal Lead, Constant P/N
^ Switch OFF ignition.
^ Disconnect TCM.
^ Connect test box to TCM wiring.





^ Switch ON ignition.





^ Connect voltmeter across #29 (TCM A29) and #44 (TCM B14) on test box.

If reading is approx. 5 Volts:
- Check signal from gear selector to TCM.
If reading is over 5 Volts:
- Check lead between MFI B24 and TCM B14 for short-circuit to supply.
If reading is below 5 Volts:
- Check lead between MFI B24 and TCM B14 for open-circuit.





Checking Signal Lead, Constant R/D/3/L
^ Switch OFF ignition.
^ Disconnect TCM.
^ Connect test box to TCM wiring.





^ Switch ON ignition.





^ Connect voltmeter across #29 (TCM A29) and #44 (TCM B14) on test box.

If reading is approx. 5 Volts:
- Check signal from gear selector mechanism to TCM.
If reading is below 5 Volts:
- Check lead between MFI B24 and TCM B14 for short-circuit.