c.boots

ok need some help and info my 93' 240sx coupe with ka24de has a missfire and my rpms have been dropping when it goes into neutral. ive had the rpm dropping problem before, i changed out iacv then it went away for about a month and came back. swapped out my knock sensor and then the problem was gone for a week. checked my grounding and it was at 30 ohms, made a grounding kit for it and it went away for month and a half. now it came back two weeks ago and the rpms drop and stay down until i stop or it stalls out. ive changed out a bad injector on #4 cylinder and swapped plugs, plug wires, rotor and cap. rpms still drop but not as frequent and not as bad but regardless it still drops pass 500 rpm, and the missfire is still there. any ideas fellow zilivians?