My engine overheated and I am now getting a p0300 code, is hard to start and idles rough, but seems to run fine while driving. When I notice my engine was getting hot I was in an area of the highway where I could not pullover. I kept an eye on the oil pressure gauge which remained fine although the car did get very hot and was beginning to loose power by the time I was able to pull over.

 

I would start by removing your plugs and doing a compression test. A severely overheated engine can warp a head quick.