Re: weird idle probelm when engine is cold.......

[Allan Morris <allanm@PrimeNet.Com>]

Addressed to: C. H. Lemon <br00206@bingsuns.cc.binghamton.edu>
              Quattro <quattro@coimbra.ans.net>

** Reply to note from C. H. Lemon <br00206@bingsuns.cc.binghamton.edu> 11/20/95  6:08pm -0500


> My '88 90 has a strange, intermittent idle problem when cold.  Even 
> stranger is how I can temporarily correct it.  I'd like to, however, 
> find a permanent solution to the problem.........
> 
> OK....say I start the car in the morning and drive it about 1/4 of a 
> mile.  I then have to take the car out of gear to come to a stop.  When I 
> depress the clutch pedal, the revs sometimes fall below normal idle (to 
> ~200), slightly rise, then either stay at ~200 or the motor dies.  If the revs 
> stay at ~200, I can drive the car for sometime and, when idling, the 
> revs still fall back to ~200.  It's as if the idle speed has been shifted 
> down.  
> 
> The strange part of it is that I can correct the problem by turning the 
> ignition off and starting the car again.  The idle speed immediately 
> returns to normal.
> 
> Any Ideas??
> 
> Chris
> '88 90

I gather you have a 90 (not a Quattro) with a 5 cylinder - right?

I think what happening is you are losing the signal from the idle stabilizer valve (ISV) *to*  
the fuel injection control unit.  +12 Volts is delivered to the ISV, and this is modulated to  
open and close the ISV by grounding the signal through the control unit.  

This is measured with a dwell meter.  If you have one handy, connect it to the outlet wire, and  
see the results.  While cold, the ISV should show dwell, when hot not much.  The ISV allows  
extra air into the engine - adjusting the idle speed, or handling increased load when hot - like  
the AC.  To verify which wire it is - measure voltage at the ISV while the problem is occuring -  
if you find +12V, the problem is between the ISV and the control unit (or in the control unit).

I suspect your problem is in the connector to the control unit, or in the control unit itself.   
Turning the ignition off just "jolts" the poor connection - and it works again.  It may be that  
cold weather sets it off.

If you want/need any more detail, let me know.  


---------------------------
Allan Morris
Phoenix, Arizona
allanm@primenet.com
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