When the IAC is unplugged, it’s a dead fuck. It’ll do whatever the vacuum in the engine wants. Suck it in if it can, unless it’s clogged solid.
These things are old as shit. Motors full of varnish and carbon. That stuff is NO good for any motor. Regular oil changes, plugs and fuel filters once a year at least.
Pull out the IAC/AACV clean em up. If you notice a difference, but still not 100%, get a new one. Be sure to clean the passages as well.
Try spraying intake cleaner through the 5/8" hose before the throttle body. Does the car run with it off? Clean the throttle body as well.