[Vwdiesel] Strange "power surge"

[Bob Soukup]

My Rabbit Truck has something similar to the "strange power surge".  
Mine does it at idle.  The idle speed surges up then back down.  Running 
the AC or the headlights puts enough load on it that the idle remains 
constant.  The idle screw adjust is very touchy, about a half turn goes 
from way too fast idle to much too slow idle.  Any ideas on this?

Bob Soukup
'81 Rabbit Truck