vw passat v6 tdi 2.5, 2001 - lack off power - k3vdx

CAN ANYONE HELP ME IV GOT A VW PASSAT V6 TDI, ALL OF A SUDDEN ITS LOST ITS POWER, ITS AS IF THE TURBO IS NOT KICKING IN,SO I TOOK THE PIPE OF TO SEE IF THE WHEEL WAS SPINNING WITH IT WAS, I HAVE BEEN TOLD IT COULD BE THE AIR FLOW MAF SENSOR, GHANGED THAT, STILL THE SAME, ITS 150BHP, IT DRIVES LIKE 90BHP, AS ANYONE GOT ANY SUGESTIONS, THANKS