For the cabin temp sensor fan seizure try vacuuming out the sensor inlets there above the grab handles in the front seats and there's one on the dash. Put the vacuum up to it that should free them up, dust collects on the little blades like a ceiling fan at your house. Then if they are free you should be able to clear the codes.

For the rear seat arm rest open the trunk and undue the latches that lock the seatback up and fold the seatback down and look for anything that would hang up in there. You're right it might be a kids toy or dead body or something.

For the Turbo noise get a mechanic's stethiscope and listen under the hood in the general area of the noise and see if you can isolate it. Leaky hose would be my guess too.

Good luck.............. Mike '95 850T