I have a 98 USDM Forester L with a misfire when it's been sitting for as little as 2 hours, it only does it when it sits. The engine shakes violently and then it clears up and runs fine. When this happens it takes slightly longer to start. I started it up for the first time in a few months a week ago and the problem came back. I noticed that it afterfired right after starting it up. This is all leaning towards a leaky/faulty injector, but I just wanted to know if there are any sneaky/less well known causes. IE head gasket or something like that.:|