I've had trouble with poor (read: no) rotation with 2 key frames. I've had a lot of trouble with the "auto key" feature in the past. I'd manually key in 4 frames (one for each second, that's logical). If you manually key them, it's much easier to work with your animation later, because you know exactly where they are, how many there are, and how far apart they are. Autokeying doesn't seem to be very thorough. It misses a lot.