Slow acceleration, turbo lag?

Hi all, new member here. I have a 2004 2.0 d4d. When accelerating it's really slow, I can hear the turbo from about 2000 rpm but there is only a slight extra push, it's not until I get up to 3500-4000 rpm that the turbo actually kicks in and gives any extra power. Has anyone had a similar problem to this at all? Any advise on where to look first appreciated!