Idle problems 90Q (NG engine)

[Eyvind Spangen]

I'm having serious idle trouble with my 90Q with NG engine.

Main problem: It will either idle high, hunting up and down between 1000 and 
1500 rpm, or it will idle so low that it almost stalls, sometimes it does 
stall.

* I've tried cleaning the ISV, did not help. Cleaned the throttle body too, 
no difference.
* I measured the idle switch. When closed, it will stay at 18-20 ohms. Time 
to replace it?
* If I jump the connector while the idle is hunting, the idle will go down 
to 5-600 rpm or lower, and the car will stall.
* If I unplug the ISV when it's hunting, it will continue, but a bit slower. 
If I unplug it while it's low, it makes almost no difference.
* I've checked all the vacuum hoses and they all seem OK. No cracks and no 
open ends.
* I've checked the throttle basic setting.
* Injectors and injector inserts (the black plastic things) is less than two 
weeks old. The problem persisted after replacing them.
* Disconnecting the DPR when idling makes no difference at all.
* Engine feels a bit weak and mileage is not very good, about 1litre/10 km 
with mostly highway driving. It's more than before.
* The ECU fuses are OK.
* The charcoal canister valve will sometimes operate, sometimes not operate. 
IIRC, it operated all the time at idle with warm engine before this problem 
appeared.

It looks like the difference between idle hunting and the too low idle 
depends on the idle switch resistance, but it should not act like this 
anyway. I'll replace the idle switch, but that alone will only make the car 
idle at 500 rpm or stall all the time.

I have checked everything I know, but haven't found the problem yet. Any 
experience on this?

-- 
Regards,
E. Spangen