I have had lots of servo issues with my IV, but solved them with settings and a screw - explanation below.

The "micro activity" setting is key for getting rid of the hunting in the roll axis (in my airplane).  With the torque set at its maximum (255) for both roll and pitch, and the "activity" for each set at around 6-7, its a very good balance between being harsh and hunting all of the time.  I recently had a servo refurbished and when the install was complete all of these settings were off, and I had to adjust them back.  But when the mechanic reset everything, he also changed the micro activity setting to either zero or the max (can't remember).  It hunted in roll very annoyingly, and I thought it was FUBAR.  Adjusting this along with the torque got me back into the happy place.  

As for the screw - there is a shear pin that is designed to break if the torque on the servo is too high, presumably to not let the autopilot over control or fight emergency pilot input.  The bad news is that this pin was not designed for the high loads in a IV.  I have broken this pin several times in both roll and pitch, just by letting the autopilot fly an approach.  The fix was a great idea by my mechanic to replace this shear pin with a steel screw, essentially locking the servo to the controls.  I deem this safe because there are still 4 other ways to disable the autopilot (stick button, control head power, on/off switch on the panel, and circuit breaker).  I wanted to throw that out for others who might be having this same problem since we are on the subject.

Hope this helps

Bob R

N619SJ