Laguna hack has started intermittently idling a bit rough... if it was a petrol engine, I'd be looking for an ignition fault sort of feeling, but it clears with a whiff of throttle and runs fine once under way. Injector on the way out?
Check for air leaks into the vacuum hoses and check them for perishing or splitting. Check the fuel filter, is it due for replacement or if it has been replaced lately is it fitted correctly? Is the oil filler cap screwed on correctly?
Thanks for the suggestions - gives me a couple of things to try; much appreciated. Really ought to get my head around these fangled diesel things now they're catching on.... ah, right