related threads on this topic are rampant throughout this forum, do a search and see what other people are saying....this only indicates you're not the only one who thinks they have fuel problems/issues - so is it really an issue or is it just paranoya???
imho, in sydney, because of the traffic and petrol quality i would be extremely surprised for a stock rb25 to average better than 350-380km a tank. i've noticed people from victoria with extremely good fuel consumption figures, but they dont have the traffic of sydney, they probably have better fuel & it depends on the type of driving they do...highway vs city
i have a powerfc tuned to about 12:1 AFR and i will consistently hit 400km with a mix of city/highway/full throttle. before the tune i would be lucky to get 380km per tank.
unfortunately, you can't tune your ECU as its stock. you will have to get an aftermarket fuel controller (apexi safc) or replacement ecu to do this.
how many km's has the car done? if its not time ie. 50,000 or 100,000km's you might try as everyone says, re-gapping your spark plugs, replacing your airfilter element, cleaning your AFM & replacing the fuel filter.
...but otherwise, live with it! its a 6 cylinder turbo. its a performance car. performance requires fuel. having said all this, you're still doing better, from a fuel consumption perspective, than a V8 or Rotary!