Originally Posted by SonicVQ

Plugs and everything else look fine. (Did you really remove the intake just to check for oil residue in the intake?)

Don't guess at the problem. Pick up a cheap ($15-20) OBD scanner and use an app (Fusion or torque) to look at your long term fuel trims. This will tell you if you are running rich, lean or OK.

If possible, it would be good to check the fuel pressure at idle. It should be about 51 psi.