i believe the model 1980 has no control rod or bowden cable, its entirely vacuum controlled. so that means the pieces on top of the valve cover are probably important? have you double checked to make sure everything is routed correctly? is the 3/2 valve functioning? is that little plastic tooth that presses the shaft on the 3/2 valve worn down? the VCV should hold between 0 and 15" thats all it needs. its possible it may have been damaged by pulling 20" on it, but i dunno

__________________
1981 NA 300D 310k miles