Drop In Idling Speed

FAULT DIAGNOSIS, DROP IN IDLING SPEED

Prior Condition
No diagnostic trouble codes

Fault Symptom.
Idling speed drops sharply when equipment drawing heavy current is turned on, such as the AC/ACC, power steering, electrically heated rear window or, in the case of automatic transmission, when a gear is engaged.

DIAGNOSTIC PROCEDURE

1. Checking For Air Leakage
Start the engine, warm it up and run it at idling speed.
Constrict the flow of air through the idle air control valve by squeezing the air hose with a pair of pliers or the like. Idling speed should drop sharply. Do not squeeze the hose so hard that the engine stops.

If engine speed drops, continue with point 2.

If engine speed does not drop, continue fault diagnosis by checking whether:
- The throttle is maladjusted.
- Air leakage (after the throttle) occurs.

2. Checking Idle Air Control
Remove the constriction of the air flow.
Idling speed should rise sharply and stabilize after 10-2O seconds at the nominal idling speed of 850 rpm (warmed-up engine).

If idling is OK, continue with point 5.

If idling is not OK, continue with point 3.





3, Checking The Operation Of The Control Slide
Disconnect the IAC valve air hoses.
Remove the IAC valve.
Plug in the IAC valve's electrical connector.
Connect the Scan Tool.
Ignition switch in the ON position.
Select "ACTIVATE".
Select "IAC VALVE".
Check visually that the control slide rotates freely and displays no binding tendencies.

If the slide is OK, continue with point 4.

If the slide binds or jams, change the IAC valve.

4. Checking The IAC Valve Switch / Connector
Check the valve's switch and connector visually. If necessary, clean and grease the switch / connector .
Check whether idling speed still drops.

If idling speed still drops, continue with point 5.

If idling speed is OK, continue with point 6.





5. Checking The Engine Load
Check that the Trionic control module receives the correct input signal to compensate for any changes in engine load.
Depending on the trouble, continue fault diagnosis as follows:
- Fault diagnosis, DRIVE, Drive Input Signal From Automatic Transmission
- Fault diagnosis, A/C, A/C (Cars Without ETS)
- Fault diagnosis, other trouble, continue as described below.
Fit another IAC valve that is known to be OK. Check whether the engine runs properly.

If idling speed still drops, continue with point 6.

If idling speed is OK, change the IAC valve.

6. Final Check
Drive the car on test and check whether the fault symptoms persist.

If the symptoms persist, refer to Before Replacing A Control Module.

If the symptoms have gone, the action taken to rectify the fault was correct, otherwise the fault is of intermittent nature.