I had this same problem witt my quicksilver on my 400ex(bought used from ebay). You look like an idiot blipping your throttle to get it to idle....like you are some pit racer. Mine would even open up from idle after sitting for 5-10 seconds. I spoke with edelbrorck several times, sent it back for them to look at it twice, and still it always hung right above idle. Anyway, it would never hang with the carb out, so they would tell me it is fine, but with engine vacuum, the slide would stick. They ended up giving me a heavier spring that seemed to help, but it never cured it. I ended up selling it and appreciating my stock carb.
I do have a couple ideas for you though. Like already mentioned, check your cable and lube the hell out of it. Also check the cable where it hits the wheel on the side of the carb. Mine didnt seem like it was right. I have a couple pictures if you would like to see them.