What was found
(CAN) UPON STARTING OF ENG RPM WHICH SHOULD HAVE STABILIZED AT 70 PERCENT AT IDLE CONTINUED TO ACCELLERATE TO APPROXEMATLY 90-94 PERCENT BEFORE IT STABILIZED. ATTEMPTS TO REDUCE RPM USING ENG CONTROLS WERE UNSUCCESSFUL. ABOUT 30-40 SECONDS AFTER STABILIZING AT 90-94 PERCENT RPM BEGAN TO DECREASE ITSELF & EVENTUALLY STOPPED AT 70 PERCENT. ENG SHUTDOWN TO CHECK CONTROLS & RIGGING OF ENG WITH NO PROBLEMS FOUND. IN CONSULTING WITH PERIMETER'S TURBINE SHOP THEY SUSPECTED THAT UNDERSPEED FUEL GOVERNOR WAS STUCK & NOT LIMITING FUEL FOR A PROPER IDLE SPEED. ENG STARTED AGAIN & SAME PROBLEM OCCURED BUT RPM REDUCED BACK TO IDLE WITHIN ABOUT 20 SECONDS. FUEL CONTROL UNIT WAS REMOVED & REPLACED WHICH RECTIFIED PROBLEM.