1992 Honda Civic car problem

My 92 honda civic started to act up, like it chokes and the idle drops low, but never shuts down. I replaced the o2 snsor, injectors, fuel filter, disturbutor, tune up, and checked for vaccums for leaks. lEven put in a working engine and engine computer, but still does the same thing. When it shakes and wobbles, it seens like every thing loses power. The volt meter reads at 14.5v when don't shake and 12.4v when it shakes. I tested all power wires and when it shakes and wobbles everthing drops about 2 volts. The car feels like it's about to die, but idles slowly right back to normal for a couple of minutes the does it again. Checked engine harness and ecu and everthing has power. Only thing I haven't change is the fuel pump, and alternator. Every senor on the car has been replaced including map sensor and TPS and thorttle body.

Any help
Thanks
John