Irregular Idling MC Emission Test Problem

[Huw Powell]

> 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 doubt if the ISV is implicated in the "off idle" difficulty in holding
RPM's.  It only functions *at* idle, ie when the idle switch is closed. 
Your idle switch is closing, right?

> 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? 

In the first paragraph you don't actually mention whether the car will
*idle* properly, that is, no throttle - what does it do then?

also, when it is cold, the OXS is out of the "loop" so I doubt it is
that.

I've been real helpful, haven't I?

-- 
Huw Powell

http://www.humanspeakers.com/audi/

http://www.humanthoughts.org/