First everything that the others on here have said is valid for repairing you problem (throttle plate, timing and cutoff valve) But from reading your original post, to me it does not sound like you are tuning the carb correctly in the first place. My Bentley manual is in the shop right now so I can't plagiarize it and copy the tune up instructions
but VW was specific on the correct procedure for setting the Pict 3 carb. Now as for myself with the 009 and the 34 Pict 3 carb I have always had problems with the lag time when you mash the throttle before you get a response from the carb (flat spot) but messing with the timing has normally made it liveable, even if not completely remedying the problem, but I have never had a problem with the engine actually idling that could not be traced back to vacuum leaks, the above mentioned items, or the carb itself was not tuned correctly. And I must admit that other than vacuum leaks very of the time it was not following the Bentley manual in setting up the carb. One thing I can truly advise is most if you don't have one for your year car as is truly is the best $35.00 to $40.00 you will then get one ever spend on your VW. Olspeed
66 Ghia, "Dexter" 76 flat window Beetle
It's not a Car it's a VolksWagon!