If I let off the gas and hit the brakes fairly quickly to a stop and let off, I've noticed my idle bobling a little low. I think someone mentioned something out this being normal and having to something to do with the fuel/air supply. (not much help )
mine will idle low (500 rpms) if there has been a change in weather (temp, pressure, etc.) It usually takes 10 minutes of driving for the ECU to adapt. When it gets that low, just leave it, don't rev it up-it won't die.
Celica's idle between 600 and 900 RMP, according to Toyota. So far there is no way to fix it, and the myth about tightening the throttle cable to fix it only works for about 30 mins, then the ECU adjusts itself back down to 600 RMP. After driving hard for a long time, such as on the interstate, then coming to a stop, it will drop down lower than 500 RMP thanks to the wonderful variable valve timing with intelligence. It will correct itself after a few minutes of normal driving.