The CEL is normal, as has been stated. Are you getting really crappy start ups? My car seems like it hates to start, sometimes, and it really is starting to piss me off. It will even stop in the middle of a crank and start back up again. I don't know whats wrong with it.
You are probably talking about the J&S Knock Sensor, which you can buy from, well I don't know the website, but lots of guys run them on RS-T's to prevent detonation. I have one and it works awesome (also running the ITC).
Did you put in the colder NGK's or the same stock plugs again?