Irregular Idling MC Emission Test Problem

[Alex Nikolic]

I am new to the Quattro list.  I am overwelmed by the amount of information 
and people involved.  Its great and I would really appreciate any help with 
my problem.

I have a late 1986 Audi 5000 CD Turbo Quattro.  In Toronto Ontario, cars now 
have to pass emission tests.  Since the car is all wheel drive it must do an 
idle test and not the usual roller (dyno) test.  My issue is that the car 
will not keep consistent rpm's between 1000-2000 rpm and between 
2000-3000rpm.  The test lasts two to three minutes at these varying 
1000-3000 rpm levels. The  motor, when held without load races up to over 
3000 rpm, where it comfortably can maintain a consistent rpm level.  
Anything below 3000 rpm tends to either climb past this mark or if the 
throttle is gently lifted, drops by several hundred rpm.  When driven, under 
load, the car does not exhibit any of these odd symptoms.  If it was a FWD, 
it would surely pass the dyno pollution test without problems.

I have checked Scott Mockrey's web site for help.  The temperature sensor 
for the Idle Stabilizer Valve has been changed (new).  The ISV valve has 
been changed with one from my other Audi Turbo (without this symptom).  The 
wiring to the temperature sensor, ISV valve and ISV control unit checks out. 
  I have even changed the ISV control unit.  The car does not have any 
vacuum leaks that I am aware of.  I have replaced or checked all of the 
lines to set the car up for the increase in boost.  The car runs 1.8 bar of 
boost consistantly (Intended Acceleration ECU / WG Spring).  It has a new 
throttle switch and multi-purpose temperature sensor.  The idle problem 
occurs both when motor is hot and cold.  Could it be the O2 sensor?  If 
anyone has any other suggestions I would be greatful.

Alex Nikolic
86 5000 CD TQ
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