Sub-par fuel efficiency
 

Hey there guys. First time poster, mostly because this is the first VW i have ever owned.

Recently bought a passat wagon, and so far, I am loving the hell out of it. Talk about a well engineered piece of equipment. Joy to drive. I have only one issue right now, the fuel economy is not as awesome as i would expect it to be. Here is the breakdown

2002
Passat - Wagon
1.8T
260K km
only getting 400km per tank
no error codes thrown by the OBD2

Parts guy at the VW dealership says that even with those kilometers, i should be getting 600km per tank, easy. So far i have tried:

new ECT sensor
new sparks
fresh oil

No significant change.

So i wonder, is this simply the fuel consumption to be expected from this vehicle at these kilometers? Or are there things I should be trying to improve it? Fuel line cleaner? Air filter? O2 sensor? Help a brother out!