hey guys i need to do something about my gas consumption. i get around 13mpg in the city and 20 on the freeway. I was wondering if i changed my oxygen sensor do you think it would help? I logged the sensors and the pre cat sensor seemed to respond fine but the post cat oxygen seems a little slow. I have seen that the pre cat sensor is the important one but would the post cat sensor do this much damage.
Also with my 1997 A4 1.8T it has 102000 miles on the clock, Thanks for the help

 

I wouldn't change anything until I got the codes read.