Does anyone know why it would be that, in the same route, with no a/c running, ( and no defrost either ) that my fuel mileage was between 16 and 21 mpg (on the dash display) and now, for many trips, it has been between 8 and 13 mpg?

It's an '03 A4 3.0 with 145K miles. .. Thanks for your input.

 

samething happened with me but i have a 1997 a4 1.8T. it has 145k miles as well, it used to be 27 to 29 but now its 20 to 23 mpg. i have no clue why it dramaticaly changed. i tried fuel injector cleaner and that didnt do anything either so if you find a solution please message me it and i will do the same if find one. thank you