i just did the timing belt and water pump on a A3 2.0t.filled all fluids ran the car for two heating cycles.drove to the gas station turned car off pumped gas got on the road when half throttle car started to go and then back fired the it started to run rough drove it back to the shop and check the timing marks they are dead on.but now i have a check engine light with code po101 mass air. any idea what may have happen ????????