I second Mr. Roger's advice about the grounds and vacuum leaks. If you
haven't done so already, it's probably worth just replacing all the vacuum
hoses even if they don't look bad. Also, someone on this list recommended
making a "ground web" that connects both cylinders to the block and to the
frame (beneath the coil) and thence to the ECU. More good advice. I say this
because (a) these are both cheap and easy, and (b) if grounds or vacuum
leaks ARE the problem, nothing else you do will solve it. You can throw a
huge amount of money at parts and drive yourself nuts into the bargain, when
the problem was really an intermittently faulty ground or a vacuum leak that
didn't appear until the hoses warmed up, but that made the ECU go crazy in
response.