exactley the same problem with me van, its the intake. i cut mine down half way and repalced it with a silicone elbow and stainless bend, its a hell of a lot better.

ill try and get pics.

failing that. used a compressor air line, take off the diesel cap and blow down both fuel lines and re-bleed. could be be crap in the tank/pipes.

let me know how you get on.