Yesterday before I took my car in for smog testing I was able to put it on a scanner @ my friends work . My mileage has dropped quite a bit. I am getting about 11 mpg on this 305 tbi. I did the following about 11 months ago
1) plugs
2)completed distributor overhaul
3)oxygen sensor
4) timing set @ 0 btdc
Here are my results from the scanner
hldrpm 1000 o2 (mv) ranged any where from 920 to 350
intergrator was mostly jumping up and down from 127 to 129
tps. 52
Iac 30
esc 0
knock 0
coolant 223 f map (8.0) hg
mat 140 f map v. .88
asynch pulse no

My car passed the smog test . I figured with the drop in gas mileage
that I would have failed the test . I only smell the gas on a rare occasion .
I took off the air filter and thats where it is more noticable .

The idle on the car holds steady with a jump about 100 rpm up and down @ stop lights.

One thing I have not changed in 15 years since I have owned this car is the fuel filter . I know it should be done and will be done this weekend. Can the fuel filter cause a drop in mileage? Other thing I looked @ testing was the map sensor . The coolant sensor was swapped out a while back . The car starts up never has issues or stalls . So i was stumped what is making the mileage just drop. This has been going on for about a 8 months. Just been to cold in wisconsin to want to tinker on it.

Dynodan

 

I can't fathom how a restrictive filter would cause a rich condition and lower mileage. Wait another few weeks. The weather is improving. May even be in the 50s next week.