Yeah, I don't find P0623 anywhere, even with the online service that came with the scanner. Anyhow, the 300 code is basically worthless...I KNOW the car is missing. Sheesh.
I've checked vac lines and electrical connections...no dice. I just went out to see if I had spark at all of the cylinders, but it'* now running perfect...So now I can't even trouble shoot this stupid thing the old fashioned way.
I hate cars sometimes.
EDIT: My frustration about the misfire code isn't with you telling me what the code said, but with the vague information from teh code.