Best thing to do is perform some basic checks, such as plugs and wires, then go from there. Some things already mentioned, check for vacuum leaks, check any wiring that was disturbed, and I still say to try another MAF, if one is available. Backfiring could be a sign of too rich a fuel mixture, as unburnt fuel is being ignited in the exhaust. This comes back to the codes, lean conditions in both banks, the ECU thinks it's running lean then richens up the fuel mixture, so much that the backfire occurs.
