evap fault the noise is the carbon canister removing excess fuel from the system, I cant understand why there is no fault code which is normally the canister purge valve

 

Possibly the battery getting low on power????
But if you are pretty sure you have a problem with fuel pressure, that may as well be the culprit (or the battery is not providing enough juice to pressurize the system while cranking etc.)

Brian

 

Both my A4 and my A6 have the same problem(both 2.8 motors). This problem seems to occur on a lot of the motors. First I showed bad temp sensor on the engine code, I replaced it, the check engine light went out but still have the problem. The next thing to do is clean out your throttle body. These motors are bad about getting build up on the backside of them. Get to your throttle body and use a moist towel or cloth to wipe of the backside of the throttle body and that has helped tremendously.

 

Something similar happened to my 99 A6 2.8 avant about a year ago. I took it to Northern European Automotive in Concord NH and they did a service called "motor vac." I'm not exactly sure what it consisted of but it solved the problem. You can probably email or call them if you want to pursue. Just google the name of the shop and you'll get their contact info (i think it is www.northerneuropeanautomotive.com)

 

I wanted to let anyone know who might be searching for similar conditions that I finally fixed the problem.
I bought a complete used fuel rail (including injectors and regulator) for $100 and put it on. Problem solved!
The problem had to be something wrong with one of the injectors. I know thanks to a fuel pressure gauge, the regulator was working fine.

I had the injectors "professionally" cleaned at a local fuel injection shop. Who knows exactly what they did, maybe it was something stupid like the wrong voltage[:@]

Anyway it now purrs like a kitten and I am very happy. This must be the single hardest thing I've ever had to track down on any car in my 25+ of working on cars, it only took 4 months. Even a local repair shop that specialized in Audi's didn't find anything wrong to the tune of $350.

Thanks for all the ideas of things to check.