Either remove fuse F2 in the passenger compartment fuse box or the negative battery cable for 10-15 minutes.
Either will clear the keep-alive memory and will restore all the data tables to defaults.
If your PCM was re-programmed by a tuner or a similar device, that is a different matter.
If your original owner's manual is missing, download a soft copy from www.fleet.ford.com
under the PARTS AND SERVICE tab.
1995 Mustang GT Convertible, only 68K miles.
2000 Ford Contour Daily drive.
2001 F250 SD, 6.8L, 4 X4.
2007 Mercury Mariner AWD - Wifey's daily driver