My '09 2.0HDi has an annoying little issue!

It drives very nicely....when on the throttle. If I'm on the over-run, for example when going downhill, there's an annoying 'stuttering' that feels as if the fuel is being cut off, almost like a misfire...its particularly bad if I touch the throttle very lightly.....its fine if I press the accelerator harder, which I tend not to when going downhill!
Is there any sort of valve/sensor somewhere that might be misbehaving?
Pete
Nocto Diuque Venamur.