I was getting very bad fuel economy like you (350-400 km) until my front oxygen sensor died completely. seems it was dying a slow death and not working right for a long time before any noticeable symptoms showed up, i guess the ECU made valiant efforts to compensate but that must have resulted in an over-rich mixture. Since changing the O2 sensor, i've suddenly been getting 600-650 km on a tank, and i drive aggressively in the city + short hwy trips mostly. Got a long road trip coming up soon, i cant wait to see what kind of HWY only mileage i get while driving for max economy.
I read somewhere that Audi recommends changing the O2 sensors every 2 years, i guess there's a good reason for that. I saved enough on fuel after 4-5 fill ups to pay for the $130 O2 sensor.

 

Which O2 sensor was changed?

 

the front one. (i.e pre-cat)

 

I have the 2008 S5 and the tank is 65L, the S4 Tank is 70L.
I am getting 500Km on a full tank and thats with me driving pretty hard. You guys may want to check your O2 sensor and Gas filters.

 

2006 A4 2.0T
I averaged 6.7L/100km traveling from Toronto to Algonquin Park with 95% HWY driving on cruise control. I only did 5km over posted speed limit at all times. My cruise range was around 800KM without running it bone dry. Mind you there was no traffic delays, just smooth cruising.

 

dude i get like 700km in my TT ????on $50 of 94oct

what RPM are you @ when @ 120kph im @ 3000 in 6th gear

also im 8.2L per 100km

 

Well its good to see that I'm not the only one getting 350km on a tank. I've had my car for a year and half, just thinking that the quattro system made it thirsty.

No codes are being pulled, no fuel leaks, and always run good gas.

I love the car and was recently in a debate about getting rid of her partly because of poor mpg.
Definetly going to price out the O2 before the cat, and get that fuel filter replaced.

 

I'm getting about 10L/100km with 60% hwy....it seems like it's good cuz the city is the killer with the 3.0...I try not to go over 110 on the hwy...but it's hard driving an audi @ that speed...the odd time I'll push going 140-150..I think that's the best speed for it

 

I get about the same with my 1.8t 2004. Our 2002 1.8t auto is about 20% worse but my wife is more of a leadfoot than I am!! How much worse should the Automatic be before I think about changing the 02 sensor?

 

I have a 1998 Audi A4 2.8 Quatro and i only get about 400kms city and maybe 450 with 75% highway. And also i am having troubles with my gas gage. Its very inaccurate. When i fill it up it it says its full but it quickly runs down to empty after only 300 km and then i drive it for another 100 km while on empty before filling it up again. Anyone else have this problem.