I just went through this issue with an 09 4,1 Mac pro using Apple care!
I ended up getting a new Bluetooth card and antenna first, to no avail!
I ended up getting the processor, daughter board, & ram changed on 2nd attempt, to no avail.
Third time around, they changed the entire enclosure, and the Motherboard. This time it fixed it!
If you have apple care keep on them and you will get a new machine practically!