Tach sensor issues?

I've had the ERR F5 message so following what others have suggested, I played with moving the tach sensor back and forth a little at a time. I actually had it going for about 3 minutes and then it would stop again. Several more trial and errors later and I'm stumped. The last couple of times where it went about 3 minutes, it would actually speed up slightly (on it's own) and then quit. Not much but noticeable.

Ideas?