I have a 1987 fx16 gts with a small port swap. When I got the car it was idling at 2000 rpm. Things I have done:
1) blocked off iacv because it was stuck. this brought me down to about 1500 rpm when hot (1000-1100 when cold). On occasion it will wander up to 1600 and the ecu will cut fuel causing that bouncing idle thing.
2) looked at the idle adjustment but it was already all the way in.
3) deleted all non necessary vacuum components one by on. non seemed to reduce the idle.
4) cleaned all intake components.
5) tested tps according to the manual. (harbor freight volt meter)
6) blocked off power steering.
7) every other test i can find on the internet.

conclusion:
I am thinking maybe the throttle body is worn out around the throttle plate letting too much air past.
I would love it if anyone had any other ideas.

Sounds like too much ignition advance.

Check the ignition timing. First loosen the distributor and turn it clockwise until
the rpm's drop to around 900. Wind the idle air screw out some and repeat with the
dissy. Then tighten the dissy and check the timing without jumping the diagnostic
plug. You should be at 16-17 deg BTDC. Wind the idle up a bit with the air screw
so that it starts when cold, and done.

Cheers... jondee86