Idle drop by 500 rpm?

It's 12 years old. Seen some dragging, and a few years of street use, daily, I'd hate to think i killed the Throttle shafts...what's odd is the Darn thing, after following RustyRatRod and Mattax instructions, to a t, she fired up and idled at 650, then dropped to 450 in gear.. then I tweaked the idle mix screws out, that raised the idle... checked w/ a light, timing was to advanced, so I retarded the timing. At some point, I gave it a little gas, and got a pop outta the primaries. SOB never idled since... Thanks Kim, hope all is well, Chuck
With your engine combo and converter the idle speed in park should be more like 850 -875 rpm.