[Shotimes] Cutting out???

[Mike]

Strange symptom:  while driving down the road the engine momentarily dies,
tach dives, then immediately recovers.  Somewhat comical, lurching down the
road.  It will stall at idle, but start right up again.  Also, it is erratic
in nature; I'm only driving short distances till I get it fixed, and some
trips it won't do it at all.  No apparent consistency; hot, cold, or between.
Since the tach dives, I'm thinking its electrical in nature; but doesn't throw
a CEL or code.  The crank sensor was changed at a 60K about 20K miles ago, but
I've had one go out and the symptoms were quite different.  Since it always
starts right up, probably not a cam sensor.  What happens if the DIS becomes
erratic; or has anyone had a crank sensor do this sort of thing?  Any other
ideas?  ('91)  No recent maintenance, that might have caused this, by the
way.
Mike