My 84 exhibited similar symptoms.  It turned out to be the engine
grounds.  I suggested this to my mechanic when I brought it in, since I
had read on the list about how important it was to keep the ground
connections solid. He wasn't interested and went about methodically (and
expensively) checking everything, he even had me replace the ECU with a
known good one.  He had my van for about three weeks.  Finally he called
me up and said it was fixed.  He said that the final things that he tried
were cleaning the grounds and replacing the fuel pump relay and that one
or both of these fixed the problem.  My money's on the grounds.

Brian
84 Westy