What was found
MIA - FLT 331 - ON CLIMB-OUT MIA AT 6500 FEET WITH CLIMB POWER SET, AND 250 KNOTS AIRCRAFT YAWED RIGHT AND DID NOT RESPOND TO YOKE IMPUTS. AS WINGS WERE LEVELED AIRCRAFT PORPOISED VIOLENTLY FOR APPROX 5 SECONDS. DECLARED EMERGENCY AND RETURNED MIA WITHOUT INCIDENT. REPLACED UPPER AND LOWER YAW DAMP COUPLER. REPLACED RIGHT SIDE ELEVATOR POWER CONTROL UNIT. SYSTEM GROUND CHECK NORMAL OPERATION. (M)