MK2 Golf- Problematic Auto choke

I have a 1989 MK2 VW Golf 1800 carb. And since reaching the winter period in England l have been having problems. Starts fine every morning and as usual revs about 2000 RPM until it reaches temperature, but unlike normal where the revs drop to idle level they increase slowly until it's revving at 3000 RPM and as you are driving along it will be like in cruise control. Throughout a journey the revs will drop after a while but then later for no real reason sundden pick up and be revving high which is usually noticed when stopping. I managed to have a look whilst it was revving high and the accelerator cable was not tight so it was the cable getting stuck!! I pushed down on the plate near where the wax stat is and lowered the revs with great resistance and the revs just returned. It can't be a sticky butterfly valve as the revs wouldn't have returned like that!! Any help would be great or any ideas would be much appriciated! Can't leave it revving like that, can't be good!! (very embarrasing too lol) Kind regards Brett