Misfires are usually the result of a problem with the plug wires or spark plugs.
Remove the underhood light bulb, and start the engine in a dark garage. Lightly mist water or window spray over the engine. Any arcing in the mist indicates wires with cracked insulation. Replace the wires.
If the spark plug boots are covered with oil, the plug tube seals are probably leaking where the valve/cam covers connect to the heads. This can cause a short. Remove the valve covers, put a thin layer of high temp silicon on the plug tube seals, and put it all back together. In severe cases, the plug tube seals should be replaced first.