TD5,uneven running / misfire ????

hi, now and again my disco (99) seems to be running very uneven, more prominent when cold. it sometimes clears quite quickly but has been known to last the full 13 miles to work..
i have changed the fuel filter but i am now wondering about the engine harness !!!
any advice pleae..would this be picked up if plugged into a diagnostic pc ?
thanks ..

Hi, ive had 3 td5s now and ive never had a prob but a good friend had the same fault and it turned out to be ECU probs...Id get it plugged in and checked.