Right on, he could do a power balance test, to see if it's just one cyl. (indicating plug/wire/injector/etc. pertaining to one cyl) or random misfire (indicating the ignition/injection/etc. system as a whole).
Like dmorris said, sometimes it's hard enough to pinpoint an intermittent problem in person let alone on a bulletin board. Try the power balance test, and try to narrow it down and see if it's just one cyl that's the culprit.