Poor mileage/plugs indicate lean running/13-16MPG (avg 14mpg)

[dwanca at att.net]

Took out the car for a ride in the mountains.  Instead of watching the Turbo Boost I changed the trip computer to MPG.  Going up I-70 out of Denver using the Boost I would expect lower mileage but not less than 17 MPG.  It is about a 30 mile drive one way going up.  Car runs great boosts well 1.8-9 BAR in O.D. passing everything.  Coming back is 30 mi of down hill 6 to 7% grades all coasting.  Best I could get was 16MPG at the end of the ride.  It came up from 14.5.  Ran between 2500 and 3200 RPM and nursed the gas for mileage on the way home.  In 60 miles I burned 1/4 tank.
Last look at the plugs indicated that the motor was running lean :? 
Checked the carbon canister frequency valve (N80)and I know that it is bad as I was supposed to get a 0 ohm reading across the connector posts per Bentley's and I got 289 ohms.  But I can't believe that this would make mileage go this bad as it is supposed to have a manual override if the solenoid fails.
So where is all the gas going?
It had a new 02 sensor installed by the PO but the fuse was not hooked up.  It passed emissions with flying colors.
I hooked up the fuse and then the cats turned to powder inside :?  I gutted them since I have 2 years before another test and no extra cash to replace cats now. 
Does anyone have any ideas about what might be wrong?