If either the upper or lower intake gasket were leaking?

On a 1995 s-10 blazer would it cause it to run rich? It is a 4.3 motor I replaced the long block in my 1995 s-10 blazer with one from a wrecking yard. The motor runs but runs rough at idle and surges. I have checked all the vacuum lines, replaced the fuel regulator, replaced the cap, rotor, and spark plugs. I get no check DTC or FF codes.

CE light will come on and flash occasionally but will go off while driving it. I had just done head gaskets on the old long block and replaced all the gaskets so when I pulled off the intake all the gaskets looked good so I re-used them (probably not the best thing to do but anyway.). Vacuum is running low, around 15 in. I have checked timing. There is no washing in lower intake when I pull the plenum off. I spray with starting fluid around the manifold when it is running and it doesn't "smooth" out.

When I spray starting fluid directly into the air cleaner it makes the motor run worse, in part probably because it is already running rich.

Hopefully you can help me.