Sticking Throttle Lever/High Idle

As with almost any VW problem, the throttle level sticking open (and thus the engine is not idling correctly), can be caused by any one or any combination of the following –

1. It may be that the accelerator cable connection under the accelerator pedal is not attached correctly. In my car, a PO had bent the metal piece on the end of the cable around so that it could not come loose. One day my accelerator broke while I was driving home from work, right behind that bent-around metal fitting. Attaching the properly-designed fitting to the accelerator pedal helped, but did not fully resolve the problem with a sticking throttle arm.
2. The accelerator cable may be adjusted too tightly. I found that adjusting it according to the procedure in the book (accelerator pedal all the way to the floor, throttle lever wide open, 1mm clearance between the lever and the carburetor body) resulted in a too-tight cable. Rob gave a good method that I used with success -- throttle lever against the cam, cable pulled back as tightly as possible (finger tight).
3. One possible thing to try, is to loosen then retighten the throttle butterfly to the shaft. The butterfly should self-align as the screws are tightened, but even a few thousandths out might cause it to stick. Look and the sides of the throat where the butterfly moves. You might be able to see bright 'rub' marks if the butterfly itself is binding on the sides, or on the outer edges (near where it closes). (We didn’t have this problem, incidentally).
4. The throttle lever may be sticking because the accelerator pump linkage is rubbing against the body of the alternator. In our case, though the car itself is a 1973 model, the engine was replaced with a rebuilt 1971. The PO who replaced the original '73 engine with a '71 simply put the original ancillary equipment (carburetor, alternator, etc.) back onto it, not realizing (and apparently never discovering) that the larger-circumference alternator was going to interfere with the operation of the accelerator pump. A little judicious bending of the accelerator pump linkage and slight grinding of the alternator body kinda/sorta resolved the interference problem. I finally replaced his Bocar 34PICT/3 carburetor with a Pierburg model that I bought from Aircooled.Net. This carburetor has a differently-configured accelerator pump linkage that doesn’t hang up on the alternator body.
5. When I installed the new Pierburg carburetor I also (just on accounta 'cuz) replaced the barrel clamp at the base of the accelerator throttle arm, the clamp that connects the accelerator cable to the throttle arm. I found that the fit was a little tight, so I got out my "persuader" and gently tapped the barrel clamp into the hole at the base of the throttle lever. Mistake! The barrel clamp must turn freely in the throttle lever, otherwise it will kink the accelerator cable and cause the engine to run at very high rpm. I prized the barrel clamp out of the throttle lever and reverted to the old one, which is slightly smaller in diameter and turns freely. I made sure with a healthy squirt of WD40! :-)