Rough idle, then power loss and check engine light

[proto31]

I was driving my 2003 Boxster yesterday, while sitting at a light the engine idle seemed pretty rough. I drove off and the car seemed to be loosing power and running rough. After about 20 seconds the check engine light went on. I immediately turned the car off and coasted to the side of the road. waited 20 seconds, started the car up and it ran fine all the way home. I checked with a code reader this morning to see if there were any error codes, none recorded. Any ideas, a bad coil pack?

Thanks,

Dan