Not too long ago, I had a flashing CEL problem. pulled codes P0301, P0302, P0303, and P0304. Dealership cleared all except the P0304 cyl 4 misfire. End result - a bad exhaust valve. Here is what caused the problems, and was thus responsible for a $3000.00+ repair: (notice the edge is flaked away)
It has been speculated that the valve was doomed from time of manufacture. The other valves in cyl 4 were ok, but replaced as a precaution.
And for those who missed it the first time, here's the original thread:
http://forums.nasioc.com/forums/show....php?t=1103830