intermittent jerking on Isuzu kb 260 d/c 1994

Hi all,
this is a great site,for manuals...
can someone help...?? when driving at a constant speed, cruising,no load on the engine, my isuzu jerks intermittently,like fuel starvation.whenever it does this i give it full acceleration to see if it is a fuel shortage but it accelerates contantly with no jerking at all.
i have fitted a new fuel pump and new filters,new ignition coil and spark plugs and plug wires, new distributor cap and rotor.
this problem only occurs when your road speed is constant and you are not accelerating.
what could it be????
kind regards
chris

did you clean pcv valve or the egr valve something clogged in the intake system

yeah clean all the sensors in the intake. nothing else ocurs to me.