P.s. I have EXACT symptoms you do.
My car did run like crap after o2 died though. And after replacement runs well minus the new flutter which really bugs me.
And as I said after I unplugged MAF no more flutter..
Im only guessing as you said at this point because I cant afford mechanic and know no tuners here locally.
But my guess is bad o2/maf
Or bad ecu/tune or both.
Im here for helo from knowledgable people and youre one of them. Thanks for helping and I already plan to get cobb bpv asap as well sorry ibdidnt include it