meth adds to the afr, the tuner cant see actual afr with out a wide band plugged into it. 30/70% meth with add a lot to the afr.
you need to remove fuel from the maf till your afr is in the 12's, then turn the meth on, it will lower the afr to 11's where it needs to be. from there you need to fine tune the maf some.
this is from one of my last scans from retuning meth and a N* tb with a gen5. see the bottom row, commanded afr is set to 11.4 in the tune, then you got wb error, then in red the actual wide band reading from my wide band. the wide band didnt get to 11.4 on its own. i had to make that happen.
if you just spray meth you'll be super rich on the afr and the car wont be fast at all. its rather slow when its flooding out.