Agree with Cylestyne; calibration takes time and initially, the figures are not in par with real average. Second, as you mentioned 889 Km in about 80 L, the real average turns out to be around 11 which is a little low but I believe it's nothing to do with tuning whatsoever. Mine is now 5000 Km + and giving around 14-15 in city and 15-16 on highway (not much difference, hmm). It was initially around 12 in city. So the average should improve with time.