Poor Gas Mileage 97Legacy 2.2l auto 100kmi
 

I'm getting around 22mpg. Can anyone help?

replaced plugs, air cleaner, oil change, aired up all tires to max psi

I was thinking I would do the O2 sensor next, but wanted to get opinions from ppl that know Subaru's since this is my first one. I also live at 8Kft, but it shouldn't effect a fuel injected car that much. Any ideas? Any help is greatly appreciated.

also, it runs rough at idle when in drive and car is stopped.

The MPG looks about right for that car, take a look here:

http://www.fueleconomy.gov/feg/noframes/13523.shtml

Does it run rough when you first start it, if so it wont be the O2 sensor.

Also when you say you have the tyres at max PSI, do you mean as recommended by the manufacturer, not just what the max on the tyre says?