A A319 ENG DEVELOPED A HIGH VIBRATION CONTROLLABLE ONLY AT FLT IDLE. AN EMER WAS DECLARED WITH A DIVERSION TO A NEARBY ARPT.

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WHILE CRUISING AT FL370 THE CAPT NOTICED THE LOWER ECAM WAS FLASHING THE VIBRATION READINGS FOR THE #1 ENG N1 AND THE READINGS WERE FLUCTUATING FROM 5.0 TO 9.9. THE LIMIT ON THE FLUCTUATIONS IS 5.0 SO THE CAPT NOTIFIED THE FO AND THEN SENT A MESSAGE TO MAINT TO CONFIRM THAT THE READINGS WERE SERIOUS AS THOUGHT BY THE FLT CREW. THERE WERE NO OTHER ENG INDICATIONS OF ANY PROB WITH EITHER ENG AND THE ACFT WAS NOT VIBRATING WHATSOEVER. THE CREW CONTACTED DISPATCH AND NOTIFIED THEM OF THE INTENTION TO DIVERT TO ZZZ. AT THE TIME OF THE DECISION TO DIVERT; THE ACFT WAS APPROX 30 NM W OF ZZZ1 AND THE CREW ELECTED TO DIVERT INTO ZZZ EVEN THOUGH ALMOST DIRECTLY OVER ABC AS IT WOULD HAVE TAKEN AS LONG TO DSND TO ZZZ1 AS IT WOULD TO HEAD TOWARDS ZZZ WHERE THERE WAS MORE SUPPORT FOR THE ACFT; THE CREW; AND THE PAX. THE FO BROUGHT OUT THE AIRLINE MANUAL AND CHKED THE PROCS FOR A HIGH VIBRATION INDICATION. THE AIRLINE MANUAL HAD THE CREW REDUCE PWR UNTIL VIBRATION REDUCED AND THE FIRST TIME THE CREW REDUCED PWR TO 73% N1 BEFORE THE VIBRATIONS REDUCED TO A MORE NORMAL 1.0 READING. SOON THEREAFTER; THE VIBRATIONS ROSE BACK TO THE 6.0-9.9 RANGE EVEN AT 73% N1. THEN THE CREW REDUCED FURTHER TO IDLE BEFORE THE VIBRATIONS READ IN A NORMAL RANGE. SOON AGAIN THE VIBRATION READING ROSE TO AN ELEVATED RANGE. THE CREW NOTIFIED THE FLT ATTENDANTS AND PAX OF THE DIVERT; DID NOT HAVE THE FLT ATTENDANTS PREPARE BUT JUST PREPARE FOR A NORMAL LNDG. ATC CLRNC WAS OBTAINED AND AN EMER WAS DECLARED. THE #1 ENG WAS REDUCED TO IDLE BUT LEFT RUNNING UNTIL IT WAS SHUT DOWN AFTER AN UNEVENTFUL LNDG AT ZZZ. ALL IN ALL; THE ENTIRE CREW; DISPATCH; MAINT; ARPT CRASH CREW; AND THE PAX PERFORMED FLAWLESSLY AND IF I HAD TO LEARN ANYTHING FROM THE EVENT; I LEARNED THAT IN ANY ABNORMAL SITUATION SUCH AS THIS; START THE APU; AS IT IS A VITAL TOOL IN CASE OF WORSENING SITUATION AND POSSIBLE PWR LOSS. OTHER THAN THAT; I FEEL THE EVENT WAS HANDLED IN STRICT ACCORDANCE TO PRESCRIBED SOP AND THE AIRLINE MANUAL WAS THOROUGHLY COMPLIED WITH BY ALL INVOLVED.