With Sudden Load Demand

Symptom Of Fault.
Idling speed drops drastically when the engine has to cope with a sudden load demand in connection with the engagement of high-current electrical equipment such as the A/C, ACC, power steering, electrically heated rear window or, on cars with automatic transmission, selection of a gear position.

Conditions.
No diagnostic trouble codes.





Diagnostic Procedure.
1. Check for air leakage
- Start the engine, warm it up and then run it at idling speed.
- Constrict the flow of air through the idle air control valve by pinching off the air hose using a pair of pliers. Do not restrict the flow of air so much that the engine stalls.
Idling speed should drop drastically.

Has engine speed dropped?
YES:
^ Continue with point 2.
NO:
^ Continue fault diagnosis by checking: Incorrectly adjusted throttle air leakage (after throttle). Rectify as necessary and continue with point 6.

2. Check idle speed control operation
- Remove the pliers constricting the flow of air.
Idling speed should increase sharply and then stabilize in about 10-20 seconds at the nominal speed of 850 rpm (warmed-up engine).

Functionality OK?
YES:
^ Continue with point 5.
NO:
^ Continue with point 3.





3. Check operation of the control valve
- Disconnect the valve's air hoses.
- Remove the idle air control valve.
- Plug in the idle air control valve's electrical connector.
- Connect an ISAT scan tool.
- Ignition switch in ON position.
- Select "ACTIVATE".
- Select "IAC VALVE"
- Check visually that the valve rotates without tending to bind.

Is the control valve OK?
YES:
^ Continue with point 4.
NO:
^ Change the idle air control valve and then continue with point 6.

4. Check the idle air control valve switch and/or connector
- Carry out a visual check of the control valve's switch and connector. If necessary, clean and grease the switch and/or connector.
- Check whether engine revs continue to dip.

Does the engine still dip?
YES:
^ Continue with point 5.
NO:
^ Continue with point 6.





5. Check the engine load
- Check that the Trionic control module receives the correct input signals to compensate for any changes in engine load. Depending on the trouble, continue fault diagnosis with:
^ Fault diagnosis, DRIVE.
^ Fault diagnosis, other trouble. Continue as described below.
- Try changing the idle air control valve.
- Check whether the idle air control valve works.

Do engine revs still dip?
YES:
^ Continue with point 6.
NO:
^ Change the idle air control valve and then continue with point 6.





6. Final check:
- Clear the diagnostic trouble code.
- Perform a driving cycle:
- Drive the car at varying engine loads and rpm for 5 minutes.
- Car speed should exceed 12 mph (20 km/h) at some time during the driving cycle.
- Stop the car, apply the handbrake and run the engine at idling speed. '
- Switch off the A/C and all electrical equipment. If the car has automatic transmission, select position P.
Allow the engine to stabilize its idling speed for 10 sec.
- Switch on the A/C and all electrical equipment. If the car has automatic transmission, select position D. Allow the engine to stabilize its idling speed for 10 sec.
- Evaluation of driving cycle: Check whether diagnostic trouble codes P0505-P0507 have been generated.

Has any of the diagnostic trouble codes been generated?
YES:
^ Continue at the idle air control valve, DTC P0505, P0506, P0507.
NO:
^ The remedial measure taken was correct.