I recently bought a 2005 F650, with about 70K miles. After setting for a few hours, the engine having cooled off, it will start normally, but then has no usable power until it has idled about 10 minutes. It will barely move around in the yard, and certainly is not ready for traffic during this time. But after that 10 minutes, it seems to have normal power for driving and highway speeds. What could be causing this?