Hi Guys,
I have recently installed a new Holley Truck Avenger 670 on my GMC. I was replacing an old QuadraJet with lots of missing parts. The intake is an unknown Performer with the multi/dual flange for spread-bore/square-bore. Looks like the one here.

The original QuadraJet had an adapter plate like this.
I left this off and bolted direct to the manifold.

The truck is running great--fires right up, lots of power, no hesitation.
My problem is a very high idle, even with the curb idle screw all the way out. I tried the trick of spraying carb cleaner at the base but-NO Change in idle. Do I need a sealing plate for this intake to run a square-bore Holley? Thanks for any ideas guys.

update===So Holley techs said it sounded like a vacuum leak, recommended the carb cleaner test, and to call Edelbrock about needing a sealing plate for this intake.-----Edelbrock support said flat out "No you don't need a plate or adapter for that intake." I kept on , asking "what about older performers", but he seemed sure I didn't need a sealing plate.
So back to square one- it seems.