i have tried everything to remedy my poor fuel economy of 430km per tank of gold gas. here is what i have done, if you see something i may have missed please let me know. (95 850 turbo - 145km)

-no codes from engine, no excessive smoke from tail pipe
-new plugs, wires, rotor, and distrabuter
-new O2 sensor
-replaced vacuum elbow near power steering pump, this raised the fuel economy from 400km to 430km per tank, other elbows seem ok
-new tires, that are properly inflated
-no visable fuel leaks
-cleaned the throttle body
-have used two full bottles of amsoil fuel injector cleaner
-unplugged the batterie for 1/2 hour to reset the computer
-K&N air filter which i had cleaned and re-oiled, could this have messed up the mass air flow sensor? if so how can i check it, would it not send a code?

i am puzzled as to why the fuel economy dropped from around 540km per tank and has been so consistently achieving this poor consumption. sometimes at when idling the rpm will drop and nearly stall before catching up again, this is the only odd thing that i have noticed as the car still has full power and does not lag on acceleration.