stuttering throttle

Can anyone help I have a 2002 2.2 diesel x-trail that has developed a fault, it has started to stutter when driving along, it feels has if the engine is cutting out then it cuts back in and revs up back to the position it was before without any movement of the throttle pedal, I'd you accelerate as it picks up it will then keep accelerating OK but if kept a constant revs of around 2000 rpm it's just seems to cut out and back in again as your driving along. It is very reluctant to go up hill unless you get it revving quite highly first and slip the clutch on a high revs but if you have to stop in hill it's very reluctant to pull away. It started doing this a little a couple of days ago then has fine until today when it has been very bad and just keeps cutting out and then back on again all the time