What was found
EMERGENCY DECLARED, LT ENGINE VIB 2.6 WITH CLB, Z-POWER, ALTITUDE 17,000, EST, PERFORMED QRH ENGINE VIBRATION, 72.18, RETARDING THRUST. RETURNED VIBRATION TO NORMAL LEVEL, HOWEVER VIBRATION APPEARED TO SLOWLY INCREASE AS FLT PROGRESSED WITH CRUISE POWER. AT LOW POWER SETTING ENGINE WAS WELL WITHIN LIMITS. REPLACED LT ENGINE VIBRATION MONITOR UNIT. BITE CHECKED GOOD REF MM 77-31-00, LOG PAGE 642889 FOR OPS CHECK.