Flight Crew Air Transport Pilot (ATP)
Confusion; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Executed Go Around / Missed Approach; Flight Crew Diverted
Aircraft
Upon arrival at destination and after careful planning for a low visibility approach throughout the flight due to forecast conditions; the Captain set up for CAT3 approach. On the approach with Approach Armed and 3 autopilot's  engaged 'No Autoland' was annunciated. Autoland Status was reset and 'No Autoland' went away.  On approach with Loc and Glide slope captured 'Land 2' was annunciated. Go around by the Captain; with autopilot engaged was commenced due to downgrade. While following Tower instructions for go around; we began experiencing degrades in the automation that did not present any EICAS messages but created confusion and problems with 'what is the aircraft doing now' type of concerns! We leveled off at 3000 FT and set up for CAT 3 Land 2. While receiving vectors with autopilot engaged; the flight director/autopilot  would only command 5 degree bank in turns. Due to concerns of unknown system faults causing problems and the inability to trust the automation for another approach attempt; the crew elected to divert.  We then requested deviation to ZZZZ which was CAT1.  During climb the autopilot stopped capturing altitude and at one point we missed our level off by 200-300 FT. Attempting to reset some unkown fault and non-EICAS displayed system failure; the Captain and First Officer tried to reset the system multiple times.  They turned off Autopilot and both Flight Director's twice; tried each Autopilot; to try to reset the system but it did not work. Each time the automation would restrict turns in Heading Select to 5 degrees AOB despite attempting the auto or 5-25 degree settings.  The autopilot and flight director had difficulty maintaining or capturing altitude. We set up for Cat1 ILS. On approach; LOC captured but when Glide slope was about to capture; the pitch annunciation went blank and Glide slope did not capture. At that moment; the plane also pitched up. We then flew  the approach manually to landing using raw data. On touchdown; the spoilers did not deploy (they were armed) and were deployed manually.  None of the faults were annunciated except the downgrade to Land 2. 1. Make sure aircraft maintenance does not dispatch aircraft with questionable automation and keep the aircradt better maintained to a level so this incident does not happen.  2. When operating with degraded automation; increase attention to any deviation of operating parameters.
B757 First Officer experiences an Autoland downgrade during a CAT III approach and the Captain goes around. The autopilot displays bizarre behavior while setting up for another attempt and the crew elects to divert to an airport with CAT I weather.