Re: '82 urquattro idle problem

[Robert Houk - WorkGroup Server Firmware <Robert.Houk@East.Sun.COM>]

   My '82 urquattro does not want to idle smoothly.  It tends to fluctuate
   ~200 rpms up and down, from around 800 rpms to about 1000 rpms.  Also, it

That's not totally out of keeping with mine, tends to "wander" in a
range of about 100 RPM-wide. Bear in mind the idle is a purely-static
"throttle" setting, so any change in load (e.g., the radiator fan
coming on) will substantially affect the idle RPM. The only ECU con-
trol over the idle is a Swift Kick in the Anatomy whenever the idle
drops below 820RPM (stock "B" ECU code) [gooses the timing to, ah,
encourage higher idle RPM]. Personally, I have found the UrQ engine to
be much happier at a slightly-higher idle RPM, I've adjusted my ECU
code to target 940 RPM as the trigger point, and statically set my
idle to 950-1050RPM (fully warm, 45% duty-cycle [statically set a
touch rich, but no effect on warm/closed-loop operation], no load and
in particular, no radiator fan spinning -- that's good for 100RPM all
by itself).

   intermittently stalls when idling or when returning to idle from higher in 
   the rpm range; this occurs regardless of whether the engine is hot or
   cold, although I think it might be slightly more prevalent when the engine
   is cold/warm.

   I have checked the idle and WOT switches, and they are both working fine
   (less than 1 Ohm resistance).  I have adjusted the frequency valve duty
   cycle such that it fluctuates around 50% at idle, and the oxygen sensor
   appears to operate normally around 0.5v.  The duty cycle also reads
   around 40-55% when driving normally under vacuum or non-WOT boost pressure.
   When the car is at speed and under WOT, I get a duty cycle of 75.x%.
   If I trip the WOT switch at idle, the duty cycle reads 48.8%.

Dead bang on.

   I don't have any other driveability problems that I have noticed (aside
   from what I believe is an occasional overboost cutout), and the engine
   pulls ~16InHg vacuum at idle (VD0 boost guage...although it might be off
   by 1-2InHg).  I have two good engine-to-chassis ground straps in place,
   one of which is at the intake manifold ground point for the ECU.

   Just once I happened to catch the frequency valve duty cycle when the
   engine stalled after returning to idle.  It appeared to read much lower
   than normal (around 30%, I believe).  I am not sure why this might have
   happened, unless the ECU drops the duty cycle when in deceleration
   conditions (i.e. throttle closed but rpms > idle threshhold).

   Any ideas, aside from "Welcome to urq ownership!"?

Um, corollary to "Welcome..." -- "Drink Heavily"

I had a similar problem with mine; turned out to be an itsy bitsy tear
in the hose from the metering box to the turbo inlet (looks like a
small screwdriver attempted [well, succeeded, actually] to gain carnal
knowledge of the hose).  The little flap remained usually/mostly
closed and the car idled just fine; sometimes the flap would do what
flaps like to do, namely flap and the idle would "stumble", sometimes
outright stalling. At anything over idle, the tiny hole made no over-
all difference and the engine ran great. So look for a tiny inter-
mittent air leak.

The 30% duty cycle would indicate the ECU is attempting to lean out
the mixture, although a one-shot reading doesn't mean all that much.
It's possible that something in the fuel system is causing pressure
pulses, over-enrichening the mixture, but unless it was GROSS over-
pressure (actively flooding the engine), I would expect most such
events to yield a higher RPM burst, rather than a drop.

An electrical intermittent (dropped ignition pulse, dropped pulse to
the Freq Valve) could result in both a "stumble" and/or a transiently
overly-rich mixture.

I hypothesize that a dirty/marginal injector might have the same
result -- erratic fuel delivery to one (or more) cylinders, with a
more pronounced affect at idle than under high speed (high pressure
fuel delivery).

[I could also hypothesize -- with more than a little personal history
-- that your car is infected by a pissed off Audemon.  Do you have any
small children you can sacrifice? Or a handy .50 Browning that you can
threaten with?]

My bet is an air leak.

Good Luck! (You'll need it on this class of problem...)

					-RDH