Idles from 500-1000? Do you mean it has a rolling idle? Like continuosly fluctuates?
As far as vacuum leaks go, brake clean can answer that, spray around your intake gaskets: no rpm change, no leaking intake gaskets. Look at all your rubber hoses, thoroughly!
Disconnect the battery, IAC, and PCM; White/Light blue wire from IAC to Pin 83 on the PCM can be tested for resistance, Fuse 2 (20a) to Red wire to IAC can be tested for resistance. That gives you your IAC circuit. Usually if you unplug your IAC while it's running, the car should die (try it a couple times).
To be SURE on the computer reset, do half an hour on the battery disconnect if you decide to do it.
As far as the EGR goes, it's not designed to run at idle. Usually it's off idle on cruise, maybe even acceleration.
90 Hatch - "The Purple Project"