Hi I have mk2 8 valver, i usually get readings between 30 and 40mpg on longer runs, and it goes down to around 20mpg if i hammer it. It sounds like your mfa is a bit faulty, i would think you should get a better mpg reading than what you say your getting. the mpg reading on your mfa is taken from a vacuum hose on the inlet manifold that runs through the bulkhead to the back of the instrument panel on the dash, if this hose is split or has a hole in it it can cause inacurate mpg readings on the mfa, can i suggest that you check this for any defects.