What was found
LEFT ENGINE UNABLE TO CONTROL N1 WITH AUTO THROTTLES OFF. ABOVE IDLE ALL ENGINE INDICATIONS INCREASED WITH N1 INCREASE FROM AND EGT. THE FLIGHT DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE WITHOUT FURTHER INCIDENT. THE AIRCRAFT WAS GROUNDED. AFTER TEST FLIGHT AND FUNCTIONAL CHECKS, THE ENGINE FAILED AGAIN. MAINTENANCE REMOVED AND REPLACED THE LT ENGINE MEC ASSY IAW 73-94-02, AND ENGINE RUN UP AFTER MEC CHANGE 71-95-20. SYSTEM CHECKED OK.