To find bad spark plug or wire, disconnect plugs one at a time at the coil, drive the vehicle a couple hundred feet, note how badly that disconnected plug affects the running. Stop, reconnect plug wire, disconnect another one, drive another couple hundred feet, etc for all plugs. The plug/wire that, when disconnected, LEAST affects the running is the bad one.
Works after you’ve done this at idle (sometimes problems only show up under load) and examined them in the dark for sparks.
