A friend owns a 2004 Murano. Everytime she starts it, there is profuse white smoke from the exhaust. No trouble codes, rough idling, pinging,etc. She took it to service and they can't find anything wrong but suggest "bad gas", and she needs to run it all out, put more in. Well, she did and it's still smoking! Any ideas? By the way, it just turned over 40,000 miles.