code 43 problem

1993 vortec blazer
My sevice engine light comes on once in awhile and I check the code which tells me code 43, which I guess is the knock sensor. the truck is weak in power when this light comes on, but when it's off it acts like there's a turbo in it. Was wondering if this is the problem and should it be replaced, to stop this form happening? Thank you, to anyone that replys.

I dont know what code 43 is but my light comes on when i dont get my gas cap on tight enough. (click it three times) I also loose a little power when the pressure in my tank drops from not having the cap on tight enough.