2002 3.0, 6-speed and after 3 months of ownership and no fueling issues, I'm suddenly faced with blow-back when filling the car. Strong air pressure build up and residual fuel spray. The problem seems to have emerged with the winter cold weather. I'm guessing a vapor venting issue and chased filler vapor lines under the spare tire well and behind a cover that houses a molded plastic cannister (charcoal filter???). Disconnected the push lock connector and blew air into the hose with air pressure build-up in the line and fuel. Am I chasing in the right direction? Any theories as to the problem? Water condensation somewhere that has iced up? Any counsel, of course, would be greatly appreciated!

 

Yes, you are chasing the right direction. Your ice theory is probably 100% spot on since it started once it got cold out. On the canister there should be a vent solenoid. Take the tube off and see if it's clear. If you drop the unit down and take the solenoid (vent valve) off air should pass through it in both directions. It's a normally open valve (has to be powered to close). Follow the tube that comes off the valve, if that's the one you tried to blow air through but couldn't. It goes up into one of the wheel wells (I THINK it's the left side but it's been awhile). You'll need to pull the liner back to see it. Disconnect it from that end and check if it's clear, then check the piece it was attached to, etc... until you find the spot that's blocked.

I'm trying to remember exactly where the vent tube hooks to. I believe it's the leak detection pump and then there's a filter up there as well. It's been a year and a half since I worked on an Audi and it's amazing how fast some stuff gets deleted from the memory banks, lol. Hope I've been more of a help than a hindrance.
It's also POSSIBLE the vent valve has failed and stuck shut but I'd go after the ice theory first. You are on the right track.

 

Thanks for your affirmation on this quest and stand by with an update!

 

So today, having access to the car after a long absence (belongs to my son in college), I was able to disconnect the larger of the two vent tubes at the canister connection and then attempt fueling. Lo and behold, the fueling occurred without difficulty, confirming the belief that the problem is within the charcoal cannister unit. So, the next question to research is does one replace the entire unit or just the powered purge valve? And where does one locate such part/parts? I'm not finding much beyond a purge valve out there in cyberworld.