Need Suggestion

I own a Ford Focus 2001 with the 2.0 ZTEC. My concern is that when I first purchased the car in Florida and was driving it 60-75 MPH all the time, I was getting 34-36 MPG. I now have the car in Europe with me and constantly drive it at a maximum of 28-30 MPH. I have noticed my gas milage is around 8-10 MPG. I have changed everything..ie. the air filter, oil filter, fuel filter, still no go. Does anyone have any suggestions as to what I should do? The car runs great, but I was getting better gas milage out of my Chevy Silverado than this thing is now.

gasoline quality, octane maybe lower.

A few things will contribute to fuel economy. Remember your at a high elevation where the air is more dense. The weather is a factor. A vehicle will get better fuel economy in cold weather than in hot weather. And the fuel quality would be a factor. At the low speed the car is probably not running in overdrive either. This could cause the bad fuel economy. When you was running high speed you could have been cruising in OD. Stop and go driving will also cause poor fuel economy. Cruising down the interstate and then going from red light to red light will cause a dramastic drop in fuel economy. Hope I gave you some suggestions for the poor fuel economy.

Wiley

maybe oxygen sensor???

Are your conversions right?
1.64km=1mile
3.9L=1gal(US)
4.54L=1gal(imp)
If you were getting 34-36mpg before, that works out to around 9L/100km for the metric rating. That stuff is confusing. We've been metric in Canada for 25 or 30 years now and I still have to double and triple check my figures on my conversions.

"Remember your at a high elevation where the air is more dense."
The exact opposite is true. The closer to sea level, the denser the air, hence all things being equal, the higher atmospheric pressure. Also, as the atmosphere is heated, the molecules of oxygen expand and also provdes for a "thinner" (less dense) air.