If I were you, I'd take that valve cover off and see if you can tell anything from there. It amazes me that all four spark plugs are oiled. How much experience do you have working on cars? How erratic is the idle? Could you have overfilled with oil?
Timing chain skipped a tooth, got a little valve crash? Would you be able to take off the cylinder head by yourself? It sounds to me like valve seals, but all four cylinders at once?... Only if you could have over-revved it. I don't know, it's beside me. I wish I could see the car. Is there any oil residue on the block?