Why did my check engine light come on after replacing spark plugs, wires and cyclender cover?

My spark plugs and wiring and tubing on my car cylinder (99 Plymouth neon) were drenched in oil. The problem got fixed... or so I thought. The people at advanced read it on their machine before it got repaired and said cylinder 2 misfired... When driving it it surge and kinda hesitate when accelerating. Check engine light came on and off... drove me crazy. After the car got repaired, same thing (a week later, after getting off of the interstate). I even got an oil change 4 hours after it got repaired! What's wrong? I'd like to have a good idea what's wrong before I take it back to the shop and/or probably causing it. Bad spark plugs, oil pump cruddy? Help! I'm hyperventilating.