2004 A6 3.0: The car will frequently not accept gas although tank is near empty. The filler neck will not drain after perhaps accepting a quart of gas. "Bouncing" the car, parking at a pump on an incline or flat surfaces makes no difference. Once I drive the car around the block a few times and retry - even at the same pump -it acts normally and I can fill up. No gas odors, no other symptoms. Is this a vent or carbon canister problem. Don't understand the intermittent nature of it. I've asked multiple garage attendants and they look at me like I'm crazy. Suggestions anyone?

 

Sounds to me like the check ball is getting stuck in the tank full position and then when you drive it around it is jarring loose, making the fill process operational again...my b5 s4 was doing that at one time...i forced as much gas as possible and drove it for a few days...next fill up, problem was gone and has never happened again....with yours it sounds more frequent and so youll probably have to get a filler tube for the gas fank...just make sure it includes the check ball...

 

If you hear a wooshing sounds when you open the gas cap then you have an issue with the charcoal canister (probably clogged up). If not then your issue is elsewhere.