What was found
(CAN) IN FLIGHT THE ACFT YAWS BY ITSELF WITH THE AP ENGAGED OR DISENGAGED. THE RUDDER INDICATOR ON EICAS IS ALSO MOVING BACK AND FORTH SLIGHTLY. EXTENSIVE T/S WITH WIRING AND SYS CHECKS WAS CARRIED OUT, FINALLY BOTH YAW DAMPER ACTUATORS WERE REPLACED AND THE FAULT WAS CLEARED. YAW DAMPER ACTUATOR, PN DL2233M1-1, LT SN 4164, RT SN 560. YAW DAMPER, LT TSN & TSR 19153, CSN & CSR 15213, RT TSN & TSR 1772, CSN & CSR 1384.