Hyundai Repair: Need Help, hyundai accent, miss fire

Question
Its 2002 Hyundai accent 1.6 liter.  The check engine light came on with a cylinder 3 miss fire.  Changed all plugs and reset the code.  The car runs fine now but occasionally the light will flash and the car loses power this will only last about a minute then the light goes out and the car runs fine.   No code is being set when the light comes on..any help would be greatly appreciated.

Answer
Anytime the check engine lamp comes on while driving, diagnostic trouble codes should be stored.  As a result, I've got a couple questions:

1.  How did you determine no codes were stored?
2.  What does "loses power" mean?  Be as specific as possible.  For example, possibilities include "all electrical items turn off and the car stops running," "vehicle accelerates poorly from a stop," and "a vibration coupled with poor acceleration."