reply from dave:

You can check this by starting the engine and thengently wiggling
the plastic connection of the distributor (should be at about 9oclock when
looking down at it). If the engine starts sputtering, that's your
problem...
I threaded a piece of electrical tape under the connector and that
has kept the van going for 20k+ miles now... Sure beat 325 for a new
distributor.

dave

CAREFUL!

Fooling with the distributor wires while the engine is running can result
in electrical shock!