What was found
AT DEPATURE APPROXIMATLEY 5000' THROTTLES WENT TO IDLE. (AUTO THROTTLES ON) ALT ALERTER SET TO 7000'. RE-ENGAGED A/P AT 9000'. CLIMB CLEARANCE AT 12000'. AIRCRAFT DID NOT HONOR ALT. AT 20000' A/P AT ON FMS CLIMB SCHEDULE 270/.73M SET FMA AND FMS SPEED SELECT SHOWED 290/.76M STILL IN CLIMB TO 34,000. REMOVED FROM SERVICE. PERFORMED OPS TEST OF GUIDANCE PANEL IAW AMM 22-11-01-710-801A. OPS TEST GOOD. PERFORMED OPS TEST OF AUTOPILOT IAW AMM 22-11-00-710-802A. OPS TEST GOOD. COULD NOT DUPLICATE. RETURNED TO SERVICE. NO PARTS REPLACED.