A bad 02 sensor will decrease or increase the amount of gasoline fed to the cylinders and cause heat from the lean condition.. hence increasing the noX.. I havn't had the problem but have heard many times of the 02 sensor causing the problem.
The timing is computer controlled and should be where ever the computer tells it to go.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist