Edelbrock 800cfm AVS2

The metering rods bouncing at idle on an AFB/AVS causing a rich idle....goes in the same fairy tale book as the PV on a Holley opening at idle & causing richness.
Neither is possible IF the throttle blade/ t slot position is correct. The reason is that there is insufficient air flow past the almost closed blades; insufficient air flow means not enough pressure drop to pull fuel out of the booster.
Now, if the blades are open too far at idle, then there could be sufficient air flow to activate the main system. Easy to check: see if fuel is exiting the boosters at idle. I would doubt it veeeeeery much on an AFB/AVS single booster carb. I suspect that the rich idle mentioned above is because the blades are open too far at idle [ big cam/low vac ]. The engine is getting additional idle fuel from the greater amount of T slot exposed, making it rich. Mixture screws likely have little control over the idle. The fix for this problem is to add by pass air so that blades can be closed & have the correct t slot/blade correlation.