Rough Idle

Make- Dodge
Modle- Stealth R/T NA
Year- 1991
Mileage- 175,000 recent engine work, including heads.

Bought a 91 dodge stealth R/T NA last summer, ran fine for a while, then the IAC went out. I drove it for a while before I really noticed the idle problem. I replaced the IAC and now when its cold it idles around 2000 rpm and when its warmed up it idles around 600-700. It jumps slightly thought at idle, like someone is giving it a tiny bit of throttle, then it drops to 500 speeds up a little then goes back down over and over again. Also if I give it gas when its just idleing it revs up nice but when I get off the throttle right away it slows down and it almost dies, then comes back up around 600. I checked vacum lines, and the resistence on the IAC is still around 40 ohms on all pins so what else can I look for that would cause a rough idle. I also noticed that the rubber plug that goes in the idle adjustment screw was taken out so someone before me was messing with that. Does anyone know how far in or out it should be screwed at stock settings?
Thanks guys