If you pull off the intake hose and look at the throttle body, it will probably be jet black, and lots of gunk behind the throttle plate. Clean all of that out with carb cleaner with the engine off of course. Also remove the idle bypass solenoid and clean that out too with carb cleaner.
Fill up the gas tank, and put a bottle of the strongest fuel injector cleaner. Look for ones that claim to clean out the intake valves and pistons etc. Chevron Techron or Chemtool etc(love the big daddy type logo) You will probably have to run two tanks or more of this stuff to clean out the injectors, they are probably really gummed up.
New O2 sensors at $39 a piece is not a bad idea when you get a few more$$
Get a PCV and the screen and grommet from the ford dealer, the aftermarket PCV does not seal properly and makes a big oil leak :barf:
After cleaning everything out. Try clearing out the computer by disconnecting the battery for 10 min.
My car runs just fine at 10° initial with 87 octane, have not tried to bump more. I ran 15° with 93 octane just fine, it did get a little more power at the track, but not worth the $0.20 a gallon for daily driving. Most stock stangs will show up with low timing.
Oh yeah, remove that air silencer found in the fenderwell, that is a true sign of a virgin stang (mine had it still
) Get a K&N direct replacment filter, works better than most of the supposed cold air kits with the cone filter.