Hi,
This will require someone who has the tools and ability to diagnose this type of problem. Beyond trying to verify the problem, they should check all of the technical service bulletins from Audi, and verify that the vehicle has all the latest software available. They will check for any diagnostic trouble codes stored in every system on the vehicle and then come up with an idea as to what there next steps should be.
It may end up being something simple like a vacuum leak, but it could be many other issues, so it really helps to find a shop that can tackle all these other things I mentioned.
Good Luck, let us know what you find out!