[urq] Ideas for rough running continued - Solved!

[Ben Swann]

I don't know if this will help, but as I am sorting out mine presently, have
gleaned some information on the way things work with the WX engine.

One thing that you may not be aware of is that the idle control is done by
advancing the timing which is different than on the later MC Turbo and the
NA engines.  I don't recall there being an idle compensation valve/switch
that lets more air in as the RPMs drop.

In any case, these events are triggered by the primary signal output by the
hall sender - this signal/lead/wire goes directly to the F/TCU (Fuel Timing
Control Unit) and processes  this signal  in conjunction with the Speed and
Reference signals (flywheel sensors), Manifold Pressure, Coolant temp and
air intake senders to advance and retard the timing..  The processed signal
is output  to the fuel pump relay and Ignition Control Unit and presumably
the tach.

By use of the Idle Switch located on the throttle body, the Idle Stabilizer
Function of the F/TCU is switched on if the engine speed is below 820 RPM
and the ignition timing advanced/retarded to regulate the idle speed.

Again, I haven't seen any reference to an idle air stabilizer valve like in
many other cars, although there appears to be an auxiliary air valve -
probably used during warmup and simply controlled by the thermo time switch,
which is just an educated guess.

BTW adjusting the distributor will do nothing for the timing.  It is either
"in window" or not.  Of course it is good to have the distributor set so
that the hall windows are dead center, which would  be best should there be
any slop in the mechnics of the distributor.  By using the two flywheel
sensors in concert with the hall signal, the F/TCU knows exactly what the
crank position is and the signals are synchronized.

Diagrams help to explain this and the best source are the two documents
online "Audi Turbo Quattro Introductory.Service Training Information: and
corresponding "Maintenance and Adjustments". These two documents will
explain things far better than one ever could in an email.  Perhaps someone
has these links - I lost all my links in a hard drive crash and am presently
rebuilding them.

HTH

Ben

[Date: Wed, 6 Apr 2005 19:41:22 -0600
From: "Ed Kellock" <ekellock at gmail.com>
Subject: Re: [urq] Ideas for rough running continued - Solved!
To: "UrqList" <urq at audifans.com>
Message-ID: <000a01c53b12$e8fa6020$9f0a2146 at clspco.adelphia.net>
Content-Type: text/plain; charset="iso-8859-1"

I may have had an "AHA!" moment.

I went out the adjust the distributor subsequent to my weekend post
and Ingo's response to see if anything changed with my ignition
cutout.  It didn't.  The car started easily but sure enough the
ignition cutout is still there.

As I sat there opening and closing the throttle, I noticed that the
cutout seemed to occur as soon as I lifted my foot.  Once in a while
it would happen a moment later as the rpms fell.  It did it reliably
enough that I believe I can connect the behavior with the symptom.
Not high rpm's involved, most of the time it was nothing over 2500.

When the ignition cuts out, the tach needle drops every time but the
fuel gauge seems to be unaffected.  And the relay in the fuse panel
that clicks doesn't do it every time, only when the duration of the
cutout is longer.

What's the gizmo that holds the idle up a bit until the car warms, the
idle control?  I think the temp sensor for mine is somewhat defective
because the rad fan had already kicked on once before the idle control
let the idle drop down to a more normal warm idle.  As soon as this
occurred the cutout started happening by itself repeatedly but not
necessarilly enough to kill the engine.  When I opened/closed the
throttle to keep it running I found that I could reproduce the cutout
much more directly always on decel or lift throttle.

Anyway, all of this reminded me of Ingo's sticking fuel plate spring.
Now, maybe I'm pairing apples and oranges a bit here, but the
similarity is interesting at very least.

Is there any relation between the lack of air flow and resulting fuel
cutout as in Ingo's case and the ignition trigger?

Ed]