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.
- Construct 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:

^ Throttle adjustment.
^ Air leakage (after the throttle).
Rectify as necessary and continue with point 6.

2. Check the operation of the idle air control valve

- 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 900 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 connector

- Make a visual check of the control valve's switch and connector. If necessary, clean and grease the switch/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:

^ Diagnosis by symptom/Dips in idling speed and engine RPM/When put in gear.When Put In Gear, Drive Signal
^ Fault diagnosis, other trouble. Continue as described below.

- Try changing the idle air control valve.
- Check whether the idle air control valve works.

Does the engine still dip?

YES: Continue with point 6.
NO: Change the idle air control valve and then continue with point 6.





6 Final check:

- Perform a driving cycle:

^ Drive the car at varying loads and engine rpm for 5 minutes.
^ Car speed should exceed 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 either of the diagnostic trouble codes been generated?

YES: Proceed to "Diagnostic Trouble Codes P0505, P0506, P0507: Idle Air Control Valve. P0506
NO: The remedial measure taken was correct.