Bad miss, wet exhaust, 5kcstq

[Wallace White]

Fellow listers -

My '87 5kcstq developed a bad miss yesterday. It is definitely tied to
engine speed, pulsing once every two revolutions. It seems like one
cylinder isn't firing. I pulled the spark plugs; they're two years old
and show wear but none was out of the ordinary. The ignition wires all
meet the 6k +/- 1.2k spec. I put the timing light on a few of the
cylinders and saw spark; if there hadn't been, you'd think the spark
plugs would be wet anyway. So I don't see anything wrong there.

I'm troubled by the exhaust, which pulses at that same rate and puffs a
little... mist? It's not that cold out (50F?) and our other car's
exhaust is almost invisible. I stuck a paper towel near the tail pipe
and removed it to find little water splatters all over it. (Sure enough,
they've evaporated and the towel looks clean now.) Uh oh.

I haven't run the car more than a few minutes yet, but I'm continuing to
hear lifter noise. That isn't that unusual, but it does make me wonder
if I have a collapsed lifter that is keeping one cylinder from running
right. 

Maybe it's just because I talked with a friend today who blew a head
gasket, but this--especially the heavy moisture in the exhaust--has me
worried. No noticeable coolant loss, though it has had a slow leak for a
while that I've been trying to trace.

Any advice would be appreciated. Thanks. 

- Wallace
  '87 5kcstq 167k

P.S. The occasional low idle hasn't recurred yet; I was looking forward
to testing the ISV until this situation arose. Thanks for the replies on
that.