couple of problems

ok I have several problems, first my tach, when driving or sitting still the tach jumps up to 2k rpm past either from idle position or driving rpm position, but the tranny does not slip, I just had the vehicle speed sensor replaced, now I also had some codes read, they were po300 and po325, which one is the knock sensor, and the other is a misfire (I dont feel a misfire in my engine and I know how that feels and also do not hear one), now I did some trouble shooting with the factory manuals and I come to believe that the knock sensor needs replacing, but I was wondering does this sensor cause the tach to jump or/and cause a misfire or cause the pcm to believe there is a misfire?