well i had the same problem 5 weeks ago with my 77 280z, changed almost everything, plugs, wires, cap, fuel filter, fuel lines, dropped and cleaned the tank, dis timing, new msd coil and was still having the same problem, finally i got an ECU and a harness from the junkyard from a 83 zx and it runs very good now, dont think that the vac leak would cause such problem....