Have a 2000 SE Vulcan with 204K. This afternoon drove it 75 miles highway, got in city traffic and the vehicle was sitting at idle. Vehicle started running rough but no CEL at that point. Drove to destination and parked vehicle and shut off. Came out started vehicle and CEL came on. Drove to AutoZone to have scanned, both the PO 171 and PO 174 codes were discovered. CEL stayed on, was able to get vehicle home. Vehicle runs well as long as I'm on gas but when I let off gas, idle drops to < 500 Rpm and either runs rough or stalls. Any ideas--MAF, Oxygen sensor(s), or fuel injection issues?