so definitely not the pump have you done a compression test?bad injectors could also be the culprit as these little engines seem to work with very little compression (mines arounf 300PSI and still pulling strong)
I tell ya what injectors will cause some weird crap to happen as well. I'm not saying that's your problem just backing up what gigaz2 said.I just got done re ringing my engine (new pistons also) and I had this weird miss. It sounded like a Subaru with a after market exhaust system till 2000 or so where it would smooth out.I swapped in my HUGE injectors just to see and idles smooth and runs perfect now.Weird I say weird...