Originally Posted by allthumbs

I am sure that it will be fouled and cleaning could result in improvement. It does require the manifold removal which is detailed in other posts.

I get the feeling from the intermittant nature of it and the way that it changes with putting the car into Park or Neutral makes me think it is a vacuum line or something. But then I really don't know anything about cars.

Let me know how it goes removing the manifold, what you find, and how it affects the rough idle.