stalling when hot

Hi guys, new on this forum and apart from doing a std service on my partner's 2006 Sprinter 308 CDI haven't done any repairs on it. The engine keeps cutting out while driving. Initially it seemed to be when going up an incline but now it's everywhere and anywhere. No particular speed, gear or...

new to the forum so please feel free to correct any breaches of etiquette around my post I am a bit stumped by this. When hot and in drive the engine sometimes develops a very rough idle and will stall, and is usually a bit tricky to restart. Occasionally difficult to start in very hot weather...