What would cause the idle to fluctuate in between stop lights? Im not referring to the idle literally bouncing but the rpms going from 800rpm to 1000rpm back and forth. The rpms dont fluctuate while idling in the driveway or stopped at a light. The engine runs fine and strong new plugs,distributor,wires,carb etc. Its a chevy 350,Hei,600 cfm edelbrock carb, vacuum advance,almost everything is new or replaced. It almost seems like the timing advances a little or retards a few rpms. I dont believe it is a fuel problem but Ill leave that up to you guys. Any ideas?

Small vacuum leak, worn throttle shafts, mechanical advance springs too lite making the wieghts bounce around, excessive fuel puddling in the intake (common with single plain intakes) and thats off the top of my head. Check the simple stuff first, vacuum leaks, worn throttle shafts are the easiest to check for..