A week or so ago, I posted about my 87 running very rough except at highway
speeds.  Most replies concerned looking over all my connections since I had
just given the engine a lot of new parts and service.  No problems noted
there.  Dennis Haynes noted that any conditions that start out fine and then
go bad most likely lead to an O2 sensor.  OK, I have to cut and drill mine
out as it's jammed in so bad.  Only problem is, sometimes the van runs fine
and sometimes, it starts of really bad and/or has a LOT of trouble
starting/restarting.  Anyhow, here's a new thing that may tip some of you
more experienced than I into where I might need to look.  The other day I
start it up and about 2-3 minutes into it, my tach goes crazy.  The engine
is loping at an idle but the tack is at 3-4K and moving around 1K or so.  I
goose the throttle and the needle responds but it goes right back to the
3-4K range and hunts.  The whole time (except for goosing) the engine is
idling.  I take off and drive normal but the needle is staying in the 3-4
range.  After about 5 minutes, it works normal.  Haven't driven it since
then (3-4 days).  It still sputters and hesitates really bad.  It stalled on
me right smack in the middle of a busy intersection and would not restart.
Had to get pushed over to side.  It finally started about 2 minutes later.
How is it that it runs fine at highway speeds and like crap around town?
BTW, 3 different AFM's all the same problem.  New cap, rotor, wires (double
checked the order), plugs, air filter, and cleaned the AFM.  Not gas quality
as I've pumped about 15-20 tanks from different stations since this
started.

Confused in FL

TJ