If your pre cat 02 sensor is bad, the car will idle and run poorly. Have you changed it?

I would also go ahead and pull the IAC, thoroughly clean it, and reinstall. I had idle issues in the past, and cleaning up the IAC worked like a charm

1999 Eclipse GS
Built motor
Hahn 16G Turbo w/ FMIC
Hahn Stage 5 Portfueler (270's & 500's)
Zeitronix Zt-2 wideband w/ 3.5bar MAP
3" SS Turbo Back
CM Stage 4 Clutch and Fidanza Flywheel
Baer Big Brake Kit