Intake minifold gasket leaks are common on the early Explorers.  White smoke
at startup could mean it's trying to burn some coolant along with the
gasoline.  Sometimes, from what others have said, when it warms up it will
stop leaking (at least as much).  Possibly it's leaking more once you get
going but it doesn't sound to me like that would account for the engine
running THAT poorly.  Plus you'd probably notice a significant coolant loss.
Keep in mind that I'm no expert, just another guy that has some Explorers
who has (so far) always managed to fix them.  I was thinking maybe a stuck
thermostat but that also doesn't seem like it would cause the engine to crap
out.

What I was refering to was the cluster of vacuum lines on the intake.  If
you have a leaking vacuum diaphram on the automatic transmission it could
cause the vacuum connectors to swell up and leak.  You can pull a couple of
connectors off and see if there is any red trans fluid on the inside of
them.  But, once again, burning a tiny bit of trans fluid doesn't seem like
it could make the engine runs so rough.  BTW be careful with the small
vacuum lines as they can break easily.

To me it's now sounding like a bad electrical or vacuum connection.  Take a
really good look at the battery cables, especially the positive one.  They
can be completely deteriorated on the inside and look OK on the outside.

Since you have a code telling you that cylinder one is acting up pull out
the plug and see if it has coolant on it.  You might also want to have the
cylinder pressure checked.

There was a recent argument, er, I mean discussion about adding Stop Leak to
our engines.  My personal opinion is that it is unlikely to help with an
intake manifold gasket leak but it might help a lot with a head gasket leak.
It also might clog your heater core or thermostat.  I used about 1/4 of a
can of Justice Brothers (or something like that) stop leak that was supposed
to stop head leaks.  In my case it seems to have worked.  The first time I
used a whole can and had to flush the radiator and heater core.  And clean
the thermostat.

I have replaced the intake manifold gaskets on both my '91 and '92.  I just
followed the instructions in my Hayne's manual and labeled everything,
especially the plug wires.  The first time it took me a few days working on
it now and then.  The second time it went fairly quickly though there is a
lot of stuff that has to be removed.  In both cases it was successful.  On
my '92 it had white smoke and ran rough and idled poorly.  On my '91 it was
gushing out so diagnosis was simple.

I've not had any fuel pump problems (yet) but when you said it cycles
"sometimes" are you trying it right after it just cycled?  I'm thinking it
might not cycle because the system is already pressured at that point.