I had this high idle issue with my '83 cabriolet and, as John Walker suggested, it was my own doing. When I pulled the engine for a top-end rebuild and resealing, I went through all the CIS components for cleaning and checking.

I know I reset the throttle body stop when I disassembled and cleaned the throttle body because that 99.9 percent closure "looked" awfully tight (but there were no signs of wear).

After re-assembling everything and tuning the engine in, I found that I couldn't get my engine idle below 1,000. This had me scratching my head and looking for air leaks, etc.

Finally, I re-adjusted the throttle body plate stop (just above the point where the plate binds in the throttle bore) and this corrected things.

Brian