Seems to be missing but passes ballance tst?

It could be missing under a load, but pass the cylinder balance test when there's no load on the engine. How recently have you replaced all of the major tune-up items (plugs, wires, cap & rotor, PCV, fuel filter, air filter)? If it's been a long while, or you can't recall it having been done, those would definitely be some good places to start. How do the plugs look? Any partial fouling of any plugs? You could also do a compression test, if the tune-up had already been performed recently and this problem still existed afterward.