Sounds like an IAC issue. When my IAC was acting up it was not noticeable at idle, but if the car was in neutral and rolling to a stop the RPM's would climb and then slowly fall back to normal once the car came to a full stop.
Pull the IAC, thoroughly clean it with brake cleaner or electric motor spray, and then reinstall it. If the problem persists OHM it out and see if it is within spec.
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