Are you thinking cam timing, or ignition timing? Cam timing being out sets a code (or it did for me) and changes your power band, usually for the worse. Ignition timing is non-adjustable but if you found a way to do it I'm sure there are lots of people here dying to find out how, as am I. Crappy gasoline can cause your car to run like a bag of $**t, did you fill up somewhere you don't normally? Also there is a knock sensor just ahead of your oil filter, on the passenger side of the engine, that may be unplugged or malfunctioning. These are just some random ideas as I have to go drink beer now. Good luck!