99 Intrepid Idling Low Problem

I have a 99 Intrepid which just recently had the engine rebuilt. Everytime the car runs for a while and gets hot, the idle will drop and fluctuate lower than 500 rpms when the car is stopped (e.g. at a stop light, stop sign, etc.). If the car is hot and I throw the car in reverse and turn the wheel hard the car will occasionally idle too low and cut off. The IAC has been changed and there are no signals being read from the ICU. The wiring to the IAC has also been checked. Someone mentioned that it could be a computer problem but my mechanic is reluctant to change the ICU because he doesn't think the computer will just fail in that one area. Is this true? Or should I attempt to have the ICU changed? Also, the mechanic had the computer flashed after he rebuilt the engine. Does the ICU need to be programmed with default codes that only Dodge can do? Could this be the source of the problem? Thanks for responding.