I've got an 86 Z31 turbo and I just got it back from the shop. The idle is at 1100 rpm and won't adjust down. I think the climate control rpm dohicky is the problem. Can someone tell me what controls the idle when you turn the ac on?

 

Have you tried unplugging the climate control and starting the car to see if the idle changes?

 

Turns out it is the AAC/FICD. I tapped on it with a hammer and it came back to life for awhile. But now it randomly drops the idle from 800 to 500 rpm, I think it is faulty. I'm going to replace it.

 

Glad to see you found the problem