Stuck throttle body ? Sounds like the mechanic is stuck, stuck on getting $ 500.00 from you.
Did he / she mention anything about cleaning the throttle body ?
A check engine code that reads " Throttle Body " could be the Throttle Body itself,,Any part that is attached to the Throttle Body,,or any part that is connected in any way to the Throttle Body by a hose or wire connection.
And if the Throttle Bodies on VW Passat's sometimes got stuck,,,then that sounds like a recall issue,,,kinda like the Toyota gas pedal issue.
I'd get a second opinion from a different mechanic at a different shop,,don't mention the first mechanic and see what the second one says.