Hello

I am really stuck with this one and I am hoping someone can give me some advice. I recently had to replace a exhaust valve in the head, it had cracked. Everything went fine and the car was running well for about 5 weeks when all of a sudden it just died on me while driving. I was able to get it started and it idled very rough and was stuck in lymph mode not allowing me to go over 2000 rpm. After sitting for a while it would start up and idle normally but if you give it some rpm's like 4500 or so when the engine goes back down to idle it studders the EML and traction lights go on and it goes back into to lymph mode. Sometimes it will start again normally or it will be difficult and start up rough again in lymph mode. I am getting codes p0070, p0300 and p1617. The trouble seems to be related to the p1617 code. Lastly I had my code reader attached while the engine was running normally and after it had its fault the reader would no longer retrieve any codes only saying "the ignition must be on" until unplugged it and turned off and on the ignition. Any ideas?

Thank you in advance.