Not wishing to hijack this thread, but I've got the same problem on an '86 Golf. Symptoms are exactly the same. Unfortunately, due not having much spare time at the time, I took the car to a local garage to take a look at. Got the car back from them and the problem seemed to have been cured. However, I suspect they either just frigged it, as having recently taken the car in for it's MOT, it failed on emissions. This garage tuned the car to fix the emissions issue, but low and behold, the cold-idle issue is back.
Presumably this is some form of carb issue? Is a replacement worth considering? Anything else to check in the mean time?
Any thoughts much appreciated.
Cheers,
Mark