A MD80 WITH THE CAPT'S ADI MEL'ED EXPERIENCED UNCOMMANDED YAW AND RUDDER FLUTTERS AFTER TKOF. THE AUTOTHROTTLE; HDG SELECT AND FO FLT DIRECTOR FAILED.

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PREFLT CAPT'S ADI FAIL FLAG ON. MEL'ED TO FLY ON AUX GYRO. WX ZZZ VARIABLE TO 2 1/2 -5000 FT RVR. DEP WX CAVU. ACFT WAS CONFIGURED TO FLY FROM THE FO'S SIDE FOR THIS LEG. IMMEDIATELY AFTER TKOF THE AUTOTHROTTLES FAILED; THE ACFT SUSTAINED A BRIEF UNCOMMANDED YAW. THE FO'S COMMAND BARS FAILED. HDG SELECT KNOB FAILED TO WORK. CAPT'S COMMAND BARS WERE OPPOSITE REQUESTED TURN. FO'S FMA WENT BLANK. DURING CLBOUT AND CLEANUP; SEVERAL FMA ANNUNCIATORS FLASHED ON FOR SEVERAL SECONDS THEN WENT BLANK AGAIN. THE AUTOPLT WAS NEVER ENGAGED THROUGH THE WHOLE INCIDENT. AT 5000 FT; NUMEROUS UNCOMMANDED 'FLUTTERS' OF RUDDER WERE FELT. THE CAPT ASKED 'IF I HAD ANY CONFIDENCE IN THIS AIRPLANE?' I TOLD HIM NO AND HE DECLARED AN EMER WITH DEP CTL. THEY WANTED TO MAINTAIN US AT 6000 FT AND FLY A HDG. WE DECLINED AND CONVEYED OUR INTENTIONS TO RETURN FOR IMMEDIATE LNDG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT THE ACFT WAS IN A HIGH RATE TURN WITH POWER IMMEDIATELY AFTER DEPARTURE WHEN THE UNCOMMANDED RUDDER INPUTS BEGAN. WHAT WAS LATER DETERMINED WAS THAT THE FO FLT GUIDANCE COMPUTER WAS INTERMITTENTLY FAILING CAUSING THE YAW DAMPENER TO ALTERNATELY REMOVE AND RESTORE RUDDER INPUT. WITH A HIGH TURN RATE THE INPUT WAS FAIRLY SIGNIFICANT AND SO AS THE RUDDER MOVED WITH THE COMMANDS AND THEN WITHOUT COMMANDS THE AIRFRAME WAS YAWING SIGNIFICANTLY.