SOLVED! 318 2500-3000 rpm idling issue. Don't think its a regular vacuum leak. Swapped 2 intakes, 2 carbs ,and 6 different gaskets still no luck.

I am having a very similar proble m with my newly rebuilt 69 340. Shot carb cleaner all over the usual suspect areas, intake to heads, carb base gasket, every vacuum port I could find. No change at idle with butterfly’s closed. The only difference is I can adjust idle with the adjusting screw but idle changes on its own periodically.
Edelbrock Air Gap manifold, Edelbrock AVS2 650, manual brakes, original distributor with Pertronics module installed, stock exhaust manifolds, stock fuel pump running around 7 psi at idle.
I need to pull and inspect the plugs, I’ll probably change them for new as these are the original from 3 years ago from the full rebuild. I’ll do that and update this post.