Loss of power / at specific rev range

Hi all

Vehicle is 2005 plate 1.9TDI Estate 150000 miles

Vehicle has developed a fault where it hesitates and falters when passing through the rev range 1600 to 2000 rpm.

It does this when either accelerating or decelerating gently or when holding a constant speed with the throttle feathered. If the throttle is opened wider (quicker acceleration) the transition through the range is smooth. it also does it when the acceleration is carried out stationary and in neutral (again with gentle acceleration) or held in the above rev range.

The car puts the engine fault light on when the above condition is endured for about 15 -20 seconds and has  has thrown up a MAF sensor code. Strangely (it seems to me) if the MAF sensor is disconnected the rough running completely clears (engine management light comes on again after a while however with MAF code probably due to a lack of input from it)

I have changed the MAF sensor but this has not made any difference

Any ideas people? All suggestions welcome !