I have made a post about this before but I now have more information. My '89 SC has an almost constant miss. However, at times the engine will run smoothly, sometimes for 100 miles at a time. Occasionally the car will transition rapidly between rough and smooth running. I first tried to replace plugs and plug wires, with no change. The problem does not seem to be temperature-related since it can start or stop whether the car is cold or warm. The check engine light is usually on when the miss occurs. The tachometer reads low while the miss is occurring, or will swing around. I have checked the connections on the DIS module, coil pack and CMP sensor. I have pulled codes 41,46, and 91. 41 and 91 deal with left and right oxygen sensors. Code 46 according to my book means "coil pack 1 circuit failure". If the coil pack was bad, would the problem be intermittent? Maybe there is a bad connection somewhere that I have not checked?