Recently i had a valve job done on it. They resurfaced the upper head as well. After getting everything back together, It ran. The engine light was still on, but i figured it was because i never reset it. About 800-1000 miles later I checked the codes and recieved "missing or bad o2, missing or bad MAF". I reset the ecu (A2) and drove it around, then cheked for faults in A2. I found none. When I took it in for smog I failed Hydrocarbon(max=85 meas=102) at 15mph, but passed at 25mph. I've read that O2 sensors can go bad and be undetected by the ecu. It has seemed to lose power on acceleration, but i thought maybe 'cause it had 140k mi on the engine. Should i try to clean the MAF and O2 sensors? How can I be sure they're in working order? What else should I look for?