Technical BBC high idle after thermostat opens?

Alright so weird scenario is happening...402 bbc, no choke, holley 4 barrel carb, new 180 degree thermostat. When the engine warms and thermostat seems to open the idle goes up from around 700 RPM to about 1100-1200 RPM. It will not go back down either.

Any ideas on what is causing it or how to fix it?

 

Vacuum leak when hot? Try tightening the carb baseplate and float bowls , maybe even the intake manifold bolts.

 

Is the throttle return spring pulling the throttle all the way back closed?