Pull the MAF element and clean it with MAF cleaner (NOT CARB CLEANER MAF CLEANER), check all vac hoses, and test your O2s with a torch and a multimeter. Multimeters are $7 at Harbor freight and everyone should have a basic propane torch for stuck bolts. Look up the how-tos on google.
Probably a bad O2.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.