Fiat: Punto Diesel Misidling

I have a MK3 punto on a 55 plate .... it has a diesel multijet
engine having done 70K+ miles ... after a good run out and engine at
normal temperature and, if, I say, pull up at a traffic lights, the idling
engine sounds just like a petrol engine which 'misses' here and there
sounding quite irregular ... the car otherwise runs fine and
consumption is well around 75mpg

is this an injector problem or perhaps an ECU problem .... anyone
offer a remedy?

thanks

omega