Help me AEU86, you're my only hope

[jondee86]

I can't speak for engines with EGR but for the UK spec (no O2 sensor)
engines I owned the items affecting idle air were these...

1. IDLE AIR BYPASS SCREW used to set the correct idle speed when the
engine was up to temp.
2. AUXILIARY AIR VALVE heated by coolant and wide open when engine cold.
Raises idle to approx 2200rpm and then tapers down to 850-900rpm
as the engine comes up to temp and valve fully closes. If cold start idle
does not act like this the AAV water circuit is likely blocked with crud.
3. IDLE-UP SOLENOID controlled (ON/OFF) by the Idle-Up computer to
compensate for extra electrical load. I believe (as stated) that this valve
is also activated by the ECU on cold start.
4. THROTTLE PLATE SETTING which controls the amount of air that leaks
past the closed plate. This is set by adjusting the throttle stop using feeler
gauges and monitoring the action of the IDL switch in the TPS.
5. VACUUM LEAKS that allow air to enter any part of the intake after the
throttle plate will raise the idle speed.

While I am sure that you are aware of these items it does not hurt to
check them off your list one at a time. Many idle speed issues are caused
by partial blockages in the AAV itself or the small water tubes and hoses.
If the AAV does not get hot enough it will not close fully and you end up
with a permanently high idle. Same effect as a vacuum leak.

Cheers... jondee86