Uneven Idling

UNEVEN IDLING

Conditions for Fault Tracing
^ No DTCs present.
^ Engine hot.

Fault Sources:
^ Faulty spark plugs.
^ Blocked injectors.
^ Uneven compression.
^ Faulty distributor cap, distributor rotor or ignition leads.
^ Faulty EGR valve.
^ Faulty sensor signals.

TESTING PROCEDURE





Inspect Spark Plugs
^ Check if any spark plug is lighter in color than the others.

If any plug is lighter in color:
- Check corresponding injector.
- Proceed to: Checking Injector.
If all plugs are of the same color:
- Replace all spark plugs.
- Proceed to: Check Distributor Cap, Distributor Rotor and Ignition Leads, section below.





Checking Injector

If any spark plug is lighter in color than the others, the cylinder in question is receiving too little fuel.
- Try with new fuel injector.
- Replace all spark plugs.
- Proceed to: Check Distributor Cap, Distributor Rotor and Ignition Leads.





Checking Distributor Cap, Distributor Rotor and Ignition Leads
^ Check distributor cap, distributor rotor and ignition leads for damage or arcing.

- Replace parts suspected to be damaged or faulty.
- Proceed to: Mechanical Check.





Mechanical Check
^ Carry out a compression test.

If compression is correct:
- Proceed to: Checking EGR System.
If compression is uneven:
- Carry out repairs as required.








Checking EGR System
^ Switch on ignition.
^ Display and read Engine Coolant Temperature (ECT) and EGR temperatures.





^ START engine and allow to idle.

EGR temperature should increase more slowly than ECT.

If EGR temperature increases more slowly than ECT:
- Connect test box to Ignition System and check ground terminals.
- Plug Ignition Control Module (ICM) into test box adapter.
- Check all signals to and from both control modules;

MFI - Engine Control Module.
ICM - Ignition Control Module.

If EGR temperature increases more quickly than ECT:
- Symptom indicates leaking EGR valve.
- Try with new EGR valve.