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.
Pay a professional mechanic w/ Dealer-level Scan Tool to thoroughly OBDII scan it: incl. Mode-6 data, Live Scan, highway driving speed test; stored & current Fault Codes, red-yellow-green: the whole Enchilada. Otherwise, w/out your scanned Fault Codes-- you're just guessing in the dark. ►Post the Codes right here.◄
Check for vacuum leak. Scotty has video on it