I'll try not to be too long winded on this but it's not easy! Check your voltage, plugs, wires, cap and rotor. Try it without the condenser. Check fuel pump pressure, volume, and vacuum. Check valve lift(bad cam). Check distributor shaft play(spark scatter). If these don't fix it pull your tming cover and check chian for slop. Sticking valves, broken springs, and blown gaskets can cause this also. EGR and manifold butterfly are suspects also. This should give you a better idea of what can go wrong. If it's an intermittent electrical problem you probably will have to wait for total failure to find it. I suspect the dist. or timing chain will fix it though. Don't forget water in the gas either. This list covers @ 95% of the symptoms you're having. Good luck & let us Know!