'86 4kq:bad miss

[sabutin@mindspring.com]

   Hi...

   A question...

   About two months ago, my '86 4kq w/90k miles on it bengan to have a
subtle low RPM stumble...nothing major, just a little hesitation. At the
same time, the engine started to surge once in a while at idle. 

   I took off the idle regulator, cleaned it, and put it back on...same
problems. I disconnected the regulator entirely, raised the idle speed a
bit. (No time or money to spare for a new regulator.) The slight stumble
remained but only in the very lowest RPM range, just a slight lack of power
at the beginning of acceleration. Otherwise, the engine felt fine.

   Two days ago, after driving the car about 1/2 hr., I parked it for an
hour, started and drove it 5 minutes, parked it again for an hour, started
it uneventfully a second time, drove about 2 minutes, and then suddenly the
minor stumble got very major. Couldn't sustain any RPMs, under load or not,
for more than a second or two. I sputtered up to my house and parked it,
figuring I'd deal w/it in the morning. 

   The next  morning, when I started it, it stumbled and sputtered for
about 5 minutes....RPMs up to about 3000, then a sudden drop to near
stalling, playing w/the accelerator would get the RPMs back up, then they'd
fall again. After about 5 minutes of this, the engine began running nearly
normally...some stumble and missing, maybe 80% normal power...and I smelled
a little catalytic convertor sulphurous kind of smell. I added some fuel
injector cleaner, drove it around my house for 1/2 an hour, and the more
the car ran, the better it felt, but never 100%. Had to go to work, parked
it again, the same thing all over again this morning.

   Any ideas? It's not likely the fuel pump or fuel filter/dirty gas, or
else why would it improve when the car warms up? Computer? Clogged cat? Any
and all suggestions welcomed.

   Thanks...