I have a '98 that had a coil issue last summer. I swapped the coil and the car ran perfect for about two months then started to slowly misfire again when idling until it degraded and started to run quite rough. I didn't feel like redoing the coil again in the cold so I let the car sit for 6 months over the winter. (from Canada eh) I started it up today to look at it and the car ran perfect??? I took it for a drive and it started to act up about 5 miles later. It ran rough all the way home but didn't throw a CEL? Any ideas? I assume a bad coil wouldn't all the sudden start working again for a while? I will try again tomorrow to see how it is running and to determine if it will through a CEL. Any ideas? Thanks in advance!!
You could also check to see if one of your fuel injectors is cutting out when the car fully heats up. Check the wiring to the injectors for any loose connections or corrosion. Any small bit of corrosion with a small amount of heat will cause a high resistance in the circuit enough to affect the operation of a certain component especially a fuel injector.
I was not so lucky. I had a cyl. 6 misfire which I temporarily fixed with new wires and plugs. After a little while, it popped back up. Pulled out the plug and dried it with some ether, put it back in and would run fine for a little while. Turns out the plug is getting wet, the head gasket is leaking coolant into the cylinder. Not good.
You have a bad valve cover gasket. No question about it. Before you put another coil pack on you need to change that gasket. Pull the plug wilres and you'll find oil on the boot (s). The oil is shorting out the coil pack