Check for vacuum leaks. I'd also recommend running some SeaFoam through your car, gas and intake. Have you checked your ignition components? I'd pull the spark plugs too to see what they look like - could indicate a problem.
I have owned an Eta for over a year, and my total average has been 7.6L/100 KM. I've gotten it below 7 during warmer months on long drives. The winter kills the efficiency by about 15%. Right now, running around 8L/100 Km.