S6 running problems, continued ad nauseum

[Steve Marinello]

Having obtained an ignition control unit/power output stage device for my S6
avant ( at a most reasonable price with the assistance of a list member), I
had hopes that the intermittent missing problem I had would finally be put
to rest.  Unfortunately, I have to report that there was no change.

The car came to me from KAR with Hoppen/MTM software mods, RS2 exhaust
manifold and RS2 injectors.  The car exhibited widely intermittent episodes
of running on four cylinders, with the culprit always being #4.  An Audi
dealer tech, the only one I let work on the urq, checked the system and was
almost sure it was a bad injector, as everything else checked out.  The coil
packs had been replaced less than 20k earlier and the dealer records seem to
point to this problem existing way back and never being fully resolved,
although it would go away for long periods.

Everything appeared to be firing correctly when the miss occurred and
disconnecting the injector lead had no effect.  Coil packs were swapped to
no avail.  The injectors were replaced with stock units, as the car appeared
to be running rich most of the time.  That was a positive step, but
unfortunately it did not cure the intermittent missing.  New plugs and new
connectors were also installed, again, without resolving the problem.
Grounds were cleaned and reattached.  The Motronic box was pulled to make
sure all the connectors looked clean and that nothing was apparent down
there.  I really had hopes for the stage device.

All I can come up with now is a problem injector lead to #4 (but it was
firing when the miss occurred and it was disconnected from the injector) or
a broken valve spring hanging up periodically.  It stinks to h*ll when it
misses, so there's plenty of gas there to overload the cats.  The fact that
it is always at #4 sort of precludes the MAF or other general system
problem, doesn't it?

The car also bucks/misses badly in 1st and 2nd when it seems to be in the
mood to shut down #4 completely.  An intermittent miss is apparent in the
idle.  Sometimes, you can trigger the full five minus one equals four
cylinder running by getting into the gas and accelerating in 2nd, 3rd or
4th.

I'm approaching a sense of despondency over what should be a very enjoyable
car.  Is this what I get for having a dependable urq?

I'm on my knees...no, actually flat on my back...can the brain trust of
these lists please provide further assistance?!

TIA,

Steve