seeking list knowledge - poor running 88 5ktqa

[Livolsi, Stephane]

Hello all, needing your help (again).
 
My 88 5kcstq (MC1 engine) is really starting to act up on me and I don't
know why.....
 
Symptoms:
1.  The biggest is hesitation and misfiring, especially under load.
Started a couple weeks ago when accelerating in 2nd gear between 2-3k
rpm, it feels like something is cutting out.  Now it's gotten really bad
and even in first gear starting off from a stop I cut some chugging and
cutting out.  Seems less noticeable/evident at higher rpm - ie, I rev up
to 4500 rpm and start off, there is less chugging if I keep the rpm up
there.  So the missing/cutout seems to be boost/rpm related.
 
2.  Exhaust is stinky.  Not in a rotten egg way, but in a heavy exhaust
smell way.
 
3.  Black soot on the inside of tailpipe, and black soot on the ground
if I idle in 1 place too long.
 
4.  Engine seems to warm up a lot quicker than it used to.  Outside
temps are admittedly warmer (+10C this morning - woohoo!) but still
seems to be getting up to quicker than last spring/summer.  (engine
working harder?)
 
5.  When it was colder in AM (couple weeks ago), it started off almost
on the first crank, would idle nice for a few seconds then idle would
die down and running would become very rough to where it seemed like
only 2 or 3 cylinders were firing.  Upon restart, it wouldn't
immediately idle but I could keep it going with part throttle
application, but the running was very rough.  After 1-2 minutes of this,
it would idle on it's own ok and reasonably smooth.
 
6.  Now when I start in AM it will not start without throttle
application and I have to keep giving it throttle to keep it idling for
the first minute or so.
 
7.  When I decelerate (ie from 4000 rpm - push in clutch and lift off
gas) the rpm will drop steadily down to about 300 then bounce back up to
about 750 where it will stay. 
 
My other car (86 5ktq) was running very well before I parked it (the 88
is the nicer of the 2 cosmetically) so I have a source of known good
used parts.  So far I have taken the spark plugs and wires off the86 and
put them on the 88 patient.  No improvement and possibly even worse
running.
Also the fuel pump is a 1 year old Pierburg and the ISV is also off the
86 car which was working well.
 
The way this came on, I am suspecting something that is gradually
deteriorating and getting worse.  But what would cause these symptoms.
What would cut out under acceleration at low rpm?
 
Any ideas gratefully appreciated.  I have looked at the SJM site and
other resources - just looking for some additional input, maybe somebody
else's BTDT.
 
TIA
 
Stephane