Well ok so here are a few contributing factor.
O2 sensor is a bad one, i changed mine got an extra 50-80 kilometers in town, more on the higway
ECU temp sensor, if that is dead, then you will be running enritched maps. See if it is within spec, there is a post on this already.
A small spark plug gap is another one, i have to run 0.6mm now and it sux on fuel, new coils with a decent gap will increasy fuel economy drasticly.
Vacume leaks, when your car is idleing hot, the vac should be about 17mmHg, see if you have Vacume leaks.
Exhaust leaks will also suck through juce, so check for those.
Apart form that, the stock ecu is dam ritch, and if you get a tuned ecu or SAFC II to take some of the fuel out, you will get more power, better fuel ecconomy and less backfire.