This is a question asked every week, but I'll gladly answer it anyways, there is a plethora of problems you can encounter with the 850, Tranny, Air Conditioning, pretty much you name, its there. But well maintained 850's are very reliable, just make sure the 850 you are buying has maintainance records, mostly make sure that the transmission fluid has been changed regularly, check for a leak in the rear main seal, and make sure the air blows cold, if it doesn't most likely its a bad evaporator. 850's are great cars, but can become costly to a second owner if the first did not keep it properly maintained. There are many more maintaince issues to check for, just look through the archives.