I posted a thread about this problem before.."all possible causes for high idle on a q-jet" and my responses narrowed it down to the fast idle cam. I was thinking the same myself because I know such a thing exists from reading service manuals. the only problem is that I don't have a clue where it is or what it looks like. I think it would be better to say I don't know jack about the fast idle cam and just start form scratch. do any q-jet gurus want to get educational on my post here??

Between the choke housing and the carb body is a lever/weight that pivots ~90 degrees between full on and full off - on being up. The bottom part of the lever is the cam itself, with an adjustment screw for the fast idle speed.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4, 2200 stall TC. Ported World 305 heads, Crane PowerMax cam. ZZ4 intake, oil pump, pan & baffle. Accel HEI SuperCoil & module. Hooker 2055 headers, 3" Catco cat & 3" catback w/dual-opposite Flowmaster. 2.93 limited slip, Spohn SFCs. AMSOIL syn lubes bumper-to-bumper. Daily year-round driver. Best ET, speed TBD...
57 Bel Air, my 1st car. '66 396, 9.7:1 forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 700 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).