Check plugs, any leaks that may cause a boost leak, did you check the diverter valve. I used my car today after the weekend work replacing 4 new coils and also put a new set of plugs in, checked my diverter valve again as i have the car remapped. Awesome driving today driving between 50-60mph, stop start round abouts, traffic lights and i am getting and average of 32mpg. I would say for me personally now that the car has reached 58k i will be doing regular maintenace to ensure efficiency. i think u need a process of elimination then work methodically from there. These engines are tfsi engines are built like nothing else.