Originally Posted by UK-Wagon
Could have been a intercooler hose popping off, but you would be able to notice that now if that were the case. So it was more likely a big backfire from improper tune/timing. If that is the case..... id be asking for my money back and finding a new tuner.
If his car backfired, he would not be driving home, as he would have destroyed many things. if it was after fire(which I believe is what you meant) then it would have been an exhaust pop(not under the hood) and would not throw a cell, as that happens post cat, where there are no more alarm sensors.
Also, over boost would through the cell, but not make the noise OP has described.
99% sure you will find, as others have suggested, that your TB hose came off. The factory ones are notorious for doing this, even with stock TMIC. Either take off the glued on end pieces, or order a replacement like the AVO.