engine idles fast then slow fast then slow, Plugs turn suty black

Enine runs fast an steady for a few seconds, then runs rough for a few seconds, back and forth.

Then after a minute or cuts off.  I pull the plugs and they are sutt black, put clean plugs in and it starts right up again.

I rerplaced the Ignition coil, and fuel regulator, which works off of vacume and is attached to fuel rail.

Originally the car would run fine for much of the time, and run slugish for a few seconds and recorver, but now it does it all the time.