If it was piston slap, I would be extremely worried about the condition of the engine! I'd say tappet noise would just be something that can be fixed by getting the tappets readjusted. Fuel economy wise, that's not excessively bad, but still could be a bit better. How do you drive the car? If you drive it fairly hard from take-off I would expect to see the economy get fairly poor though... First post here. Some of these numbers seem a bit high here. Have an Aurion Prodigy and have rarely had it above 10.5 city or otherwise. Have had the computer indicating an average of 7.3 between Canberra and Sydney. However when I first got it I thought it was a little thirsty, so had it checked - turns out #1 spark plug was a dud and had it replaced - economy improved. Only way to tell was by plugging the car into the electronic servicing gizmo. Sure the computer 'compensates' for this problem, but unless it is picked up properly like mine was, you cannot tell, such is the greatness of the engine/transmission..