My 2001 Outback Wagon has been experiencing incresing power loss. At any speed the power simply gives out. Getting from point A to point B is a very jerky experience. The car also stalls at stop signs. Two days ago a mechanic replaced the Knock Sensor. His computer showed that it was fried. The car got home without any problems. However, today it was worse than its ever been. Any thoughts?? I'm getting desperate.