Citation II Captain reported a safe landing following an incident involving autopilot anomalies that made the aircraft difficult to control.

Narrative

AUTOPILOT /ALTITUDE DEVIATION.During a straight and level flight at an altitude of 16000 feet; the Autopilot was engaged in the ALT and NAV modes ON/ ADC1.The aircraft climbed to an uncommanded pitched-up attitude and off its assigned altitude of 16000 feet; resulting in airspeed decay.The recovery maneuver involved disconnecting the Autopilot; pitching the aircraft nose down forcefully manually; and applying full thrust to the engines in an attempt to return the aircraft to its desired state. Subsequently; after multiple attempts to maintain level flight and hold an assigned altitude; Several attempts were made to reengage the Autopilot; to no avail; which would result in a pitch-high and then a pitch-low attitude. The Autopilot was disengaged; and [ATC assistance was requested].The aircraft was hand-flown using a block method of pitch and power; which limited pitch and power parameters and resulted in a descent rate lower than standard. This resulted in an uneventful landing under emergent conditions. An electrical burning smell was noted in the cockpit after landing and before shutdown.