Hello I have a 159sw 2.4ti, I have owned the car for two years with no real problems until recently it started to cut out on the approach to junctions and roundabouts for no reason. I have noticed the car runs fine from cold but when it reaches normal temp on the gauge it won't tick over it runs very lumpy if I give it just a touch of throttle only 50-100 revs more it seems to cure it is there a way of turning up the tick over I have asked my local mechanic but he says he says he cant do it.
Have you had any warning lights come on, i.e. EML? Even if you haven't I would get the ECU read just in case. Now, bearing in mind I know sweet FA about diesels I would be thinking air leaks, or blocked sensors, give them all a good clean and check pipes etc. That is what I would do before I had a little weep to myself.
Difficult to diagnose without reading any engine fault codes, I'd guess either A/F ratio or mechanical intervention. Possibly air leak around swirl flaps or faulty MAF, on the mechanical side possibly crank or cam sensors causing ECU to cut the engine due to low inertia of DM flywheel.