OK, i bought my forester a couple weeks ago and when I bought it the check engine light was on. The guy told me it was a spark plug that needed changed on the #3 cylinder. So i changed out all of the spark plugs with Bosch double platinums. The car ran a little bit better but i still noticed hesitation and lagging and the CEL was still on. I ran the diagnostics at the auto store and it told me it was a knock sensor malfunction. So i bought the sensor and came home. I took the ground off the battery first, then removed the mass air flow box. I then disconnected the wire attached to the knock sensor. I tried to loosen the bolt on the sensor but it would not budge. Bad weather was moving in so i reconnected everything in the same order in which i disconnected it. I went inside to try and figure out a way to loosen the bolt, and then my roommate got home and told me my brake lights and turn signal lights were slowly flashing and there is a clicking noise coming from under the drivers side dash. I pulled the logical fuses to check them and they were all fine. I started the car and the check engine light was off, but the clicking and lights did not stop. I turned the car off and checked the ground again to make sure it was properly tightened. I turned the key to the ON position and i heard some other clicking noises and when i turned it over the CEL was flashing. If anyone has any experience with this problem please post or PM me, I need to get this thing going.