ACFT EQUIP PROB. ENG OVER-SPEED UNCONTROLLABLE THROTTLE.

Narrative

DSNDING THROUGH FL330 THE #2 ENG OVER-SPED. THE ACFT YAWED TO THE L; THE ENG SPOOLED UP; AND THE AUTOTHROTTLES DISENGAGED. WE MANUALLY DISENGAGED THE AUTOTHROTTLES TO GET OUT OF THRUST LOCK AND PULLED THE PWR BACK TO IDLE; BUT THE RPM REMAINED IN REDLINE (N1). WE SHUT DOWN THE ENG; DECLARED AN EMER; CALLED DISPATCH; AND DIVERTED TO PHL. THE THRUST LEVER LOST COMPLETE CTL OF THE ENG: THRUST LEVER IDLE -- ENG RPM IN REDLINE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: WITH AUTOTHROTTLES ENGAGED AND COMMENCING A 'MANAGED' DSCNT; THE #1 ENG WENT TO IDLE AS IS NORMAL; BUT THE #2 ENG INCREASED RPM. THE #2 OVER-SPED AS THE RPM WENT TO OVER 100 PERCENT AND CONTINUED TO INCREASE WITH THE N1 GAUGE PULSING RED. THE AUTOTHROTTLES AUTOMATICALLY DISENGAGED AND RPTR CAPT ALSO DISCONNECTED THEM MANUALLY. TRYING TO REGAIN CTL OF THE ENG WITH THROTTLE MOVEMENT WAS UNSUCCESSFUL AND; WITH INCREASING OVER-SPEED THE FLC SHUT DOWN THE ENG. THE DEST ARPT WX WAS MARGINAL AND ACFT WAS HVY; SO FLC DIVERTED TO A CLOSER; MORE SUITABLE ARPT. RPTR SENT A SAFETY RPT TO HIS COMPANY CHIEF PLT; BUT AS YET HAD NO FEEDBACK. HOWEVER; WHEN FLYING THE SAME ACFT LATER; THE LOGBOOK CORRECTIVE ACTION INCLUDED; REPLACING THE EIU (ENG INTERFACE UNIT); BORESCOPING THE ENG AND FULL RUN-UP CHK.