If you can, get some new plug wires and try them. I had a problem that could not be detected by sight but plug wire(s) were both arcing at different times causing a rough idle. Or, a plug wire could be loose and you think it is on tight...also happened to me. If I could only see it in person! Did you happen to swap or take off plug wires and reattach wrong ones in wrong order (I have done that as well!). Sounds like something that has a very easy solution (it usually is)!