[jdl]

When the problem occurs, have a helper crank it, while you visually check for spark at the plugs. If you have spark everywhere, use a gage and check fuel pressure. Some of the national brand auto stores used to loan out a fuel pressure gage, if you don't have one. Also, use a noid lite and check for injector pulse. An intermittent rpm signal can drive you crazy?

To check for spark at the plugs, pull a spark plug wire loose, use a known good plug or spark tester in the boot. Ground metal part of plug/tester to metal part of engine, watch for spark, engine cranking.