I have a 98 Subaru Outback w/ automatic tranny. It has 107K miles. The check engine light came on about 1000 miles ago with Cyl. 2 and Cyl. 4 Misfire trouble codes. The engine also started idling very rough. I changed the platinum plugs about 4000 miles ago, so I think they're probably good. When the light came on, I checked valve clearance (it was in spec. according to the Haynes Manual) and replaced plug wires. After replacing the wires, the engine was idling normally and seemed to be alright. I cleared the engine codes and everything seemed fine. The problem seemed to come back while returning from a road trip....the engine was idling roughly and the check engine light returned to haunt me.
Even though the coil pairs Cyl 1 & 2 and 3 & 4, I replaced it just to be sure it wasn't the problem, but it's still there. The problem doesn't seem to go away when the engine is cold, warm, or hot.
Why would it work fine for a while and then suddenly come back w/ no changes?
I did take the timing belt off for the replacement of the oil seals @ the front of the engine about 4000 miles ago, but it didn't seem to be a big problem when I put everything back together. I also pulled it off about 1000 miles ago for checking the valve clearance. Is there a possibility that there could be something going on w/ the timing, crank sensor, or cam sensors, etc???