IS the oil itself contaminated? A pasty, creamy buildup at the oil cap is normal, and not a sign of a problem. If the oil itself is not foamy / "wet", then you have another problem. Have you had the codes scanned? Just b/c the CEL is not on, does not mean the computer is not storing codes. Did you ever change the plugs? If so, did you use OEM style plugs? This could explain the rough idle.

If you want to check it out before driving it more, I would do a simple oil change and see what comes out. Then, when you refill, the car should be fine for a short trip to the shop, if youy cannot diagnose the problem yourself.