My 2008 audio for 2.0 T is getting horrible gas mileage it's supposed to be getting 21 mpg in the city and the gas electronic's gauge is saying that is getting 23 mpg in the city yet I'm only getting out of a quarter of a tank 70 miles per gallon when I'm supposed to be getting a 100 miles per gallon plus I put in a fuel additive that was supposed to fix the problem and it did fix their computer problem to where the computer used to say I got 14 to 16 miles per gallon and now the computer says I get 23 mpg but the gas gauge is still going down very quickly what can I do to alleviate this problem what can the problems be and should I listen to the gas gauge or should I listen to the electronic age because the electronic gauge will say I have 400 miles left in the tank whenever I'm light less than 3/4 of the tank full whenever I should only have 285 Miles left what can I do I'm new to cars

 

I don’t know where to ask. I am looking for a quality set-top. Has anyone ordered from SwitchOnShop?