Our Forestor (1998 with 129,000 miles) began running slightly rough about a week ago. I've replaced plugs and wires and my wife said it ran better. Yesterday I put in a can of Sea Foam in the gas tank and after about ten miles the engine quit--fortunately just half a mile or so from home. I've been able to get it started for a minute many times only to have it die. This morning it improved dramatically and I took it for a drive up the mountain. I knew I could always coast all the way home if it quit. Ran real good most of the way but when I got home it began to run bad again and now it hardly runs at all. Any suggestions on resolving the problem?