Gage

Got a new 800 Holley for my LS6 clone engine. I was using a Qjet tuned by Lars with an adapter plate, put a Holley 850 on it, but it was not very responsive, idled great though. So did the Qjet. This 800 DP will idle fine, but after you drive down the street, come to a stop sign, idle will only go down to 1200 or so. You can take your finger and push the throttle back to idle, and it will idle fine, until you accel again, same thing. I tried stiffer return spring, but then the pedal is so heavy you can't open the throttle smoothly. The choke is wide open, and the fast idle screw is not touching the cam on the pass side. When the car is off, the throttle snaps back to the idle screw, but when running, it stops a little short, giving me an extra 300-400 rpm at stoplights. Kind of embarrassing at the cruise in because everyone looks at me like "why doesn't that idiot in the vette turn his idle down!!!"

Mako72

I had the same problem with my 650 DP. I finally tracked it down to the throttle blades hanging up in the bores. I had to pull the throttle plate off and with a strong light behind it, reposition the blades in the bore. It was the worst when it was cold outside, almost like driving around with cruise control on, LOL.
Just something to check, I'm sure others will chime in with other possibilities.

Gage

took the carb off the car and turned it upside down...you can see where the pass side primary plate is rubbing the the bore shiny. I sprayed some WD40 liberally and manually flipped throttle open and shut many times. Bolted it back on the car. Seems to idle down a little more, but still hanging up about 1-200 rpm above the base setting. Maybe i'll give it some time to wear down. This is kind of lousy quality. Never had this prob with Qjet or Edelbrock carbs...

Thmprr

Take the base plate off, take away any idle adjustment, then using a snug fitting flat blade screwdriver, gently slacken all 4 of the throttle blade screws (they will be burred over on the other side so don't remove them), then tap the shaft and you should see them seat in the bore correctly, then retighten the screws and reset your idle approximately. This has worked for me, so it's worth a go.