Recently, I changed my spark plugs, and noticed that one of them looked like there was obviously something wrong with it.
Here's a pic of it:
Before I could get them changed, the check engine light was on, and I had it checked. The results said that there was a misfire on one or 2 of the cylinders, and I have to change an O2 sensor. Even though I had the plugs changed, I still occasionally get the check engine light after highway runs doing over 100mph. It would helpful to get some feedback from you guys about this

 

I would first have the code read to determine the reason for the light, and the dark plug at the top looks as if it was loose and exhaust was blowing past the threads and seal.