Resurrecting this discussion. I have a similar bad idle surge. Ford 3.8L V6, plenum style manifold, Weiand 144 and a Holly 700cfm blower carb. Its boost referenced to a port in the manifold under the blower. Idle surges wildly between 800-1500 RPM, great throttle response though. We have strong vacuum that surged with the idle surge from 18inches-12 inches. No vacuum leaks, good cranking compressiion in all 6 cylinders, we've been twisiting idle circuit screws, idle set screws, etc. We can't make the surge go away either.
Has anybody had any success correcting the surge?