WHILE PERFORMING A HIGH SPEED TAXI OF A BEECH 1900; TO TROUBLE SHOOT A PW TURBOPROP PT6A-67D- #2 ENGINE; THE CAPTAIN AND FIRST OFFICER NOTICED THE ENGINE TORQUE WAS ERRATIC.

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MY FO AND I DEPARTED ZZZ1. WE DID A STATIC TKOF. I ADVANCED THE PWR LEVERS; THE #2 ENG ON THE TORQUE SEEMED TO JUMP. I LOOKED AT ALL THE GAUGES AND EVERYTHING LOOKED FINE; SO I DECIDED TO PROCEED. I THOUGHT I MIGHT HAVE ADDED THE PWR IN TOO QUICKLY ON THE GND IN ZZZ1. IN CRUISE WE WERE TALKING ABOUT THE GAUGE SOUNDING AND LOOKING LIKE IT MIGHT HAVE LAGGED A LITTLE. AND WE WERE NOT SURE IF I ADDED IN THE PWR TOO QUICKLY OR IF THE LEVERS WERE ADDED MORE ON THE L THAN ON THE R. WE DECIDED TO SEE IF IT WAS RUNNING SMOOTHLY IN THE AIR. WE TOOK THE R PWR LEVER AND MOVED IT BACK AND FORTH. THE TORQUE LOOKED LIKE IT CAUGHT (LAGGED 200 LBS). WE TRIED IT AGAIN AND IT FLOWED THROUGH FINE. THE GAUGES AND FLOW OF THE ENG LOOKED FINE. IT DID NOT LAG OR ANYTHING. I TOLD THE FO WE WOULD TRY IT ON THE GND. WE LANDED IN ZZZ2 WITH ZERO PAX THIS WHOLE TIME. I DID A HIGH SPD TAXI TO SEE WHAT THE PWR WAS DOING. WE SAW THAT THE TORQUE WAS STARTING TO SLOW AROUND 600 LBS. IT WOULD THEN CREEP TO 1600 LBS ON THE TORQUE AND THEN SHOOT UP TO 3400 LBS. WHILE ROLLING DOWN THE RWY; THIS CAUSED THE PLANE TO DRIFT TO THE R AND THEN QUICKLY TO THE L. THIS WAS NOT NOTICED IN ZZZ1 DUE TO DOING A STATIC TKOF. ON TOP OF THAT; THE LAG WAS MUCH MORE DRASTIC IN ZZZ2. IT WAS OBVIOUS IT WAS NOT AN ADDITION OF PWR TOO FAST. I CALLED MAINT CTL AND WE GOT A HOLD OF A MECH IN ZZZ2. HE LOOKED UNDER THE PANEL AND COULD NOT SEE ANYTHING STICKING. MAINT CTL THEN TOLD US TO GO AND RUN THE PLANE. WE ALL WENT ON THE RWY; DID A STATIC; AND WATCHED THE GAUGES. THEN WE TRIED IT ROLLING AND THE PLANE YAWED. RECREATING THE SITUATION; WE NOTICED ON THE HIGH SPD TAXI WHEN WE FIRST LANDED IN ZZZ2. THE MECH; MAINT CTL; AND I DETERMINED IT WOULD BE SAFE TO FERRY THE ACFT. PAPERWORK COMPLETED; WE LEFT AT XA35. DOING THE STATIC TKOF WITH NO INCIDENT.