Rough idle but drives very smooth.

First make sure the firing order is correct, and if it is, then;
With the engine idling, Go put your hand on the tailpipe so as to nearly choke it off. If it feels like every so often the engine is sucking your hand in, then one or more of your exhaust valves may not be sealing.
It could just be carbon on the seats, but it could be other things as well.