Audi Repair: 2.7T CEL and rough idle, liones, lean condition

Question
I've had a CEL for a few days now.  Codes that were thrown were P0171 and P2404.  Before I had a chance to bring it in to the shop to check it out, the car starting acting up.  I had a very rough idle and the car had the shakes along with a hissing sound like air escaping from a hose.  If I revved the engine above 2000, the car did not show any of the above symptoms.  I drove it home a couple miles and during the trip the CEL flashed the first few times on start up, but never flashed again.  The CEL is still on though and the car felt like it was about to die when I pulled it into the garage, but just idled erratically.  I appreciate your help.

Answer
I think you have a leak in the evap circuit, which is throwing your O2 sesnor off which is why you have a lean condition.  Check the liones from and to your manifold; go for the hissing sound that is a good giveaway...  Fix the leak and reset the codes, then check again.  Let me know,  Jan