Ok I have been trying to figure out why my car idles rough only on occasion. I had the hood up and it was idling rough, as soon as I shut the hood it smooths out. So when the hood is shut it idles smooth and when its up it idles rough (like it should)! WTF!!!!! I'm running a used cone K&N filter. When I take it off it runs rough though. Can anyone give me some advice? Thanks Jake T.