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?
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