29.5 mpg / 3 cyl hatchback

New fuel filter
New Oxygen sensor
New Catyilitac convertor

Car idles high other then that. No other problems.
I did fail emmisions prior to changes listed above.

What can be cutting my mpg by so much? Can the
high idle be attributed to the problem somehow?

Thanks

My Metro got about 20-25mpg before I checked the air filter and realized the seal was half way off and dirt had got inside. The timing on my belt was also completely off which I changed. Now I get 40-43mpg.

How do you know if timing is off?