I know that I had a similar problem. I called Holley and they said to back off the tiny screw that is on the bottom side of the secondary throttle shaft. Back it off flush and they turn it about a 1/8 to 1/4 turn. What happens is the secondary will pull just enough vacuum to cause the rear discharge nozzles to drip just a bit, causing a rough idle. I'm not saying this is your problem, but it never hurts to eliminate it.
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