I know on the factory Mopars when I saw a problem like that when the idle would run away or run up and down most of the time it was a TPS problem. If the idle goes up and down but returns to idle then that tells you the IAC motor is working and not stuck if it goes back to normal idle. Usually something is telling the IAC motor to run the idle up and if the TPS volts is not steady when it should be at an idle the PCM on the factory cars would run the idle up some so the car wont stall and will come down to idle nice and easy. Any erattic voltage change in the TPS will make the PCM thing you are hitting the throttle and it will flare the idle up. Course I have only worked with the stock factory EFI systems. Good luck with it , Ron