Ok, not exactly a Nissan, but in the end......

 My wife's 91 G20 runs like a champ when you first fire it up, and you can
zip around town normally until the engine reaches normal operating temp.  At
that point the car no longer maintains a proper idle, sounds like it has a
slight misfire, and most confusing to me it will idle down and die when you
step on the gas from a start.  If you take your foot off the brake and let
it start rolling, then very gently ease down on the gas you can limp it
along, if you don't mind everyone racing around you and offering the one
fingered gesture of brotherly love.  Oh yes, I almost forgot.  If you turn
the car off when it is warmed up it will not want to start, just crank.
Your options at that point are to let it cool down or pull the fuel pump
fuse, crank until the gas line is empty, then replace the fuse and restart
the car.  Here's what I've done since the problem started.

1.  All new spark plugs
2.  New distributor cap (have not replaced the rotor yet)
3.  Replaced every vacuum hose I could find, then had a friend find some I
missed and replaced those as well
4.  New fuel filter

Nothing I have done has affected the problem, with one exception.  When the
cap was replaced, the old one had two points worn clean off, now the engine
runs smoother, at least until it warms up.  All these repairs were done
AFTER the problems showed up.  Any ideas?

Thanks for any help.

Aaron