I was getting around 13.8-14.5L per 100km with my GTT, 12psi, exhaust, nistune. Changed o2 sensor, afm, fuel filter, spark plugs (1.1mm gap), all did nothing... Then I noticed the car idles a little rough, so I re-gapped my plugs to (0.9mm), clean AAC valve and reset the ECU, car idles a lot smoother and now can do about 12.5L per 100km and thats city driving.