I have a 2009 touareg tdi v6 3.0 54k miles. Perfect service history. It will run rough at start up when cold in any gear. However when I place it in reverse it will vibrate the whole vehicle hard. If you put your foot on brake and give it gas it smooths out. Problem is worse if I shift it into low range and engage center diff. When vehicle is shifted into neutral or drive it smooths out and purrs.... engine light on. Initially dealer said EGR valve needs replaced. Did that, light came back on within an hour. Now they say I need to replace the NOX sensor.... ideas?