First we need a little more info on your X. Year, engine, mileage, S/C or N/A. All this can be factors.

I will say, without the rest of the info, that it does sound like an injector or possibly a fuel pressure problem. I doubt it's knock sensor for 2 reasons. 1) A knock sensor would not retard timing on startup and then clear. 2) Knock sensors don't throw SES lights, only stored codes. Try using a scanner that has "freeze frame". That will show you all the parameters when it throws the code.

Jeff!