FYI, a fuel trim of 128 is PERFECT.......
ABOVE 128 means you have a lean condition and fuel is added....
BELOW 128 means you have a rich condition , and fuel is being subtracted....
It's impossible for the FT to stay at 128....what it will do is vary a little above/below 128......but there are limits, and when the limits are exceeded a code will set....
I have seen more harness problems than knock sensor problems....