Engine idle surges up and down when stopping at lights

Two items that may be a reach: a) check to ensure your gas filler cap is sealing. b) my old 97 460 was hard on exhaust manifold, and warped two of them on the passenger side; both time the engine ran rough until the replacements went on.
Those exhaust manifolds also spit out can bolts as the warp got worse, and could crack a head. Hope this helps,