Hello. I have a 2008 Nissan Rogue with 95,000 miles. It has a new transmission with about 20,000 on it. It idles very rough, suddenly dropping to about 300-400. It will go back up to ~900 and be fine. This is only while in park and only at idle. It runs great otherwise. I just changed the spark plugs and it still happens. What could it be? Thanks.