I have an 03 Audi A4 3.0 Quattro that wont start

What did the code say? If it was a lean code then the car needs a fuel pump and filter. The only time the o2 sensor needs changed is when it says heater circuit malfunction.

well the natural suspect would be either the fuel pump or a dirty fuel filter. but i would not rule out a fault maf sensor either start from the top and work your way down as i say. start with the spark plugs, work your way back to the coil pack. keep an eye out for cracked or worn wires but also broken plastic hoses. my old 98 a4 has a bad habbit of breaking these rubbery type plastic hoses all the time. If you have never replaced the fuel filter before do so now, and take out the mass air flow sensor and clean it with maf cleaner theroly. when i first bought my 98 it did the same thing till i cleaned the maf and changed the fuel filter

It could be the run relay, I had a VW do the same thing, dealer hunted for this problem for three years. Just a suggestion.

By any chance would you happen to know which one is the fuel pump relay ?

its either under the hood or under the dash and might be hard to remove due to its location. but its usually a square shaped short one. i think there is 2 of them in total under the dash.

Has this be solved? My 04 is having the same issue as described.

my audi A4 also start this morning with a problem itsart and idele and when i switch it of and try to start again then it start and shutdown what can that be it is a 2l tdi help please