My car has had the check in engine light on with these 3 codes almost a year. In this time experienced no change in how it drives. Now it won't pass emissions because of the codes. Ironically today as well for the first time it began acting like it was missing when in Drive at idle, but not when in neutral, and again when I was on the low range of a gear (40mph/1600 rpm).

I've looked online regarding these codes and seen how many peole have replaced the speed censor only for it to come back a few days later, same for the knock sensor.

Seeking some advise on where to start. Don't want a mechanic to bill me all along the way if this is my situation. Also trying to avoid dealer prices if I can.

Someone PLEASE provide some good advise at how to work through these issues in a sensible way.