I have a 2002 Nissan Xterra. V6 4x4. I change the oil every 3000 run mobil full synthetic 5W-30 from day one . I have 35,000 original miles. The air filter and fuel filter have been changed recently. Recently my Xterra has a pronounced bucking feeling when it's running cold. By cold I mean 8 degrees here in NH in the winter. It goes away when the truck is up to normal opperating temp. I have not changed the PCV valve not sure if that is the problem . Any suggestions would be great please. Thank you ! :banghead: