Re: Holley tuning question.
One possibility - Check your accelerator pump adjustment.
When you have turned up the idle, you are engaging the pump more, and now when you blip the throttle you get a bigger pump shot.
When you turn the idle back down, and you blip the throttle, you might have backed it off enough that the accelerator pump is no longer giving you the shot you need which is why the rpm drops way off for a second.
1972 Chevelle, 454, 200-4r non-lockup, 12 bolt 3.73
1981 Camaro Z28, 355, TH350, 3.73