[s-cars] Intermittent: Bad Idle, Stall & Black Smoke

[Keith Bedard]

Car = 1995.5 S6
Symptom = intermittent erratic idling, stalling, black exhaust smoke.
What I have already changed = coil/plug boots, fuel pressure regulator 
(FPR), O2 sensor, fuel filter

I have owned this car for about 2.5 years.  This condition has been 
driving me insane for over a year.  When I first bought the car, this 
condition did not exist - car ran perfect.  I had the ECU chipped when 
I first bought it, and for quite some time, the performance was great.  
Then it started having the strange symptoms listed above.  It either 
runs fairly well (with none of those symptoms), or it runs horrible 
(with all of the symptoms appearing at once).

I had the VAG hooked up, and one of the possibilities the VAG suggested 
was high fuel pressure (which is why I changed the FPR, which had no 
affect).  When it is running poorly, much black smoke, fuel odor, seems 
to be burning too rich.  If I accelerate hard when it is in this poor 
run mode, I will sometimes get the rotten egg cat converter smell (I am 
a little nervous to hollow out the cat - new strict emissions in 
Massachusetts will certainly make car fail inspection if that is 
done)...

We disconnected each fuel injector and saw the idle change in a similar 
fashion on each one, which proved to us that the injector, POS, coil 
and plug boot are good on all 5 cylinders.

I have heard rumors that a bad Water Temp Sensor can cause some weird 
idle conditions.

Any BTDT, would be GREATLY appreciated!

Thanks!
Keith Bedard
Templeton, MA
'95.5 S6
'87 4kq