Car running badly! on 1990 Nissan 300ZX

I have a 90 300zx NA 5spd and it is running horribly. The engine randomly misses and even back fires on occasion. The check engine light flashes on sometimes but for the most part it is not on. The things I have done to try and fix this is replace the injector connectors since they were corroded badly, replace couplers on intake to make sure there was no air leaking. I only put top quality oil and gas in my car and all maintenance is up to date. It seems when it rains the problem gets considerably worse, so whatever is causing it must be effected by humidity. When we replaced the connectors we had return voltage from all 6 injectors and the problem is more prevalent at low rps (2500-3500 rpms) but some days it does not act up at all and others it is almost underivable. Also it seems to act up when you floor it and let off the gas a little with out shifting. That is as detailed as I can get, I am out of ideas to fix this problem. Anyone have any idea what could be causing this?

Asked by for the 1990 Nissan 300ZX
start with basics. did you change the plugs, wires, cap and rotor?? common faIlures that will cause your issue. also, with a vehilce that old, the injectors make be partially clogged with debris from fuel.