If you disengage your auto pilot so it has no influence and the boat falls to starboard, it is not the AP's fault. If it is while under sail, you first have to tell us if you are on a port or starboard tack. If on a port tack and the boat falls off to starboard when you let go of the wheel, then you have lee helm (mast too far forward). If you are on a starboard tack and the boat rounds up to starboard more (or if on a port tack and the boat rounds up more to port), that is called weather helm. A certain amount of weather helm is good as it is considered to be a well founded boat in that if you were to fall overboard, the boat would just turn into the wind until it came into irons and would not sail away from you. If you have a tremendous amount of weather helm, then either your mast is too far aft (the top), or you have too much sail up for the conditions, or you are trimming your sails in too hard. If you had a swing keel, then weather helm is also partially controlled by the position of the keel (like 50% of the way up or down usually helps eliminate weather helm). Racers will also help depower a boat by moving the genoa car aft, which will make the genoa break on top first to help spill the wind.