CRJ200 FLT CREW WAS DISPATCHED WITH DEFERRED FUEL VALVE WHICH ESSENTIALLY PREVENTED FUEL BALANCING. UNEVEN FUEL BURN BETWEEN ENGS RESULTED IN EXCESSIVE IMBALANCE; AND FLT CREW DIVERTED FOR PRECAUTIONARY LNDG.

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UPON GETTING TO THE ACFT I FOUND A DEFERRAL WITH MEL. I SCANNED BACK THROUGH THE LOGBOOK TO WHERE I FOUND A WRITE-UP FOR 'R XFLOW SOV' CAUTION MESSAGE. IN THE CORRECTIVE ACTION BLOCK IT HAD 'DEFER XFLOW PUMP PER MEL.' I LOOKED UP THE MEL AND FOUND THE PROCEDURE TO DEFER THE PUMP AND VERIFIED THAT THE PROPER CB WAS PULLED AND COLLARED. I THEN READ THE PLT ACTIONS WITH MY FO AND WE WERE READY TO DEPART. PASSING ABOUT 10000 FT I SAW THAT THE R ENGINE FUEL FLOW WAS MUCH HIGHER THAN THE L. I ALSO NOTED THAT WE HAD GREATER THAN 500 LB IMBALANCE BETWEEN BOTH MAIN TANKS. I REFERRED TO THE QRH AS TO WHAT WOULD BE REQUIRED AT 800 LBS OF IMBALANCE. WE THEN ENTERED A SLIP AND OPENED THE GRAVITY XFLOW PER THE ABOVE MEL. THE IMBALANCE GOT WORSE. PASSING FL210 I ADVISED THE FO TO TAKE THE RADIO WHILE I CALLED MAINT. WE THEN GOT A FUEL IMBALANCE CAUTION MSG AND THE FUEL WAS GREATER THAN 900 LBS. I ADVISED THE FO TO RETARD THE THRUST ON THE ENGINE AND ADVISE ATC WE WOULD LIKE TO STAY AT FL230 WHILE WE TALKED WITH COMPANY. AT THAT POINT WE RETARDED THE R ENGINE TO NEAR IDLE TO STOP THE PROBLEM FROM GETTING ANY WORSE. MAINT CTL PROVIDED NO ASSISTANCE AS TO AT WHAT POINT A FUEL IMBALANCE BECOMES A SAFETY OF FLT ISSUE. IT BECAME APPARENT THAT GREATER THAN 800 LB IMBALANCE WAS A CONCERN. DISPATCH ADVISED WE DIVERT TO ZZZ. WE DID SO WITHOUT INCIDENT. MAINT CAME TO THE ACFT IN ZZZ AND CONFERRED WITH MAINT CTL AND THE MEL WAS CHANGED. WE WERE ABLE TO REBALANCE FUEL ONLY BY RETARDING R ENGINE TO IDLE AND NOT REOPENING GRAVITY XFLOW. FACTORS AFFECTING THIS: R ENGINE BURNED MUCH MORE FUEL PER HOUR THAN L DURING TAXI AND CLB. POORLY WRITTEN AMBIGUOUSLY WRITTEN DEFERRAL AND MEL. MAINT CTL NEEDS TO PAY CLOSER ATTENTION TO HOW SYSTEMS ARE DEFERRED AND ENSURE CORRECT MEL'S ARE USED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE DEFERRED VALVE IS INTEGRAL FOR FUEL BALANCING ON THIS ACFT. THE MEL AND CORRECTIVE ACTION WERE ACTUALLY INCORRECT FOR THIS MALFUNCTION WHEN THE ACFT WAS DISPATCHED. UNEVEN FUEL BURN BETWEEN THE ENGINES THEN CREATED AN IMBALANCE WHICH COULD ONLY BE CORRECTED BY UTILIZING THE GRAVITY XFLOW SYSTEM. WHEN THIS PROC WAS ATTEMPTED; THE SITUATION ONLY WORSENED. THE ONLY OPTION AVAILABLE TO THE CREW WAS THEN TO OPERATE ONE ENG AT IDLE AND THE OTHER AT MAX CONTINUOUS THRUST. A PRECAUTIONARY DIVERSION WAS THEN NECESSARY; AND IT WAS SUBSEQUENTLY DISCOVERED THAT AN INCORRECT MEL WAS INITIALLY APPLIED.