Our 2008 4.2L Q7 all of a sudden has started running very rough (still starts) and has a ton of error codes. Seems like one of these items must be the cause and the rest are symptoms. Maybe the ECM? Suggestions on where to start?

00135 Fuel rail system pressure too low
08852 Fuel pressure regulator 2 control circuit
00768 random/multiple cylinder misfire detected
00776 cylinder eight misfire detected
00774 cylinder six misfire detected
0101112 evaporative in mission system the purge control valve circuit low
05173 secondary air injection pump relay J299 short circuit to ground
05153 secondary air inlet valve N1 12 short circuit to ground
05255 Secondary air injection secondary air injection valve 2 N3 20 short circuit to ground
00258 mass or volume airflow circ low input
00268 mass or volume air flow B circuit low input
04763 fuel pressure regulator valve bank to open circuit
01314 engine control module ECM - please read DTC