Is this after a detailed check up in person? Which dealership?
Edit : if this diagnosis was reached via phone, don't change the TB yet. P2118 can be caused by accelerator pedal issues, blown fuses, wiring issues and lastly physical TB issues.
Reset the error code and drive to your nearest city / arrange an expert electrician. Since I've been through a similar ordeal, do not just replace the TB without a thorough diagnosis.
Lastly I feel dealerships are not equipped to deal with complex electrical issues - just like to work by trial and error instead of a detailed diagnosis.