I would change distributor cap and rotor. Get a Bosch. Also you can not test the cap and rotor under load, at least I can not.

This is unless you very recently did change cap and rotor.

Possibly crankshaft reference sensor, but I'd pass on that for now and do cap and rotor.

Edited
If you have a spare MAS relay you can swap them out and see if that's the problem.