Some of the upper end vehicles slip into "limp mode" when there is a problem. This allows you to "limp" back home or to the dealer. Many Audi A4 have been known to slip into this mode and the problem is very difficult to diagnose unless you at least have the OBD-II trouble code (On Board Diagnostic for a hint. Sometimes dealers will not charge you to hook on a code reader, but then others love it for you to have to make an appointment, drop off the car etc. and then charge you $50 to read off the codes and then "clear" them so the Check Engine Light (CEL) goes off... likely only to return a few hours later.
Since you are on FixYa, I'm confident that you could would make use of a code reader multiple times. Providing this diagnostic code would be very useful for us to suggest a solution. Code readers actually are not that expensive and are very easy to use... and very convenient... saving that trip to the dealer and all the delay.
You can pick up an OBD II or OBD2 scanner tool on Ebay or Amazon. There are a great range of ones with various bells and whistles, but ALL give you the basic codes. I personally prefer the all-in-one code readers rather than the 'bluetooth" ones that you have to access through an Android or iPhone. Please resubmit your question with these codes and we likely can guide you to a solution. Amazon com obd II Tools Equipment Automotive
My OBD-II scan tool is similar to this one... it's middle of the range but very, very adequate. I hope that the Scan-Tool will give you (or us) the hints we require for a solution. (NICE car BTW, once its operating properly!!! /denis