EPC warning light problem! Request for help

Hello, with our A6 4.2l Tiptronic engine: ARS we have recently engine problems! It often lights up the EPC lamp in the instrument cluster, then we have power failure... feels like emergency run! Wants to go out, etc... Error memory is much with throttle valve Poti mechanically and electrically error! At the end there is always immobilizer! The latter cannot be deleted! Keys exchanged and deleted! He drove great for 2 days and now the problem is back! Request for advice, thank you and greetings

Gerd