Just a thought, with the extreme cold we are having it takes my 1.4T double the idling time to reach the same temperatures compared even to when its 15F outside. 8-10 minutes idle my engine is not even past 100 degrees.Well, it did it again. I went out at lunch to sit in the car (like I do everyday) and after 10 mintes of idle, I blipped the throttle and had the same issue. What the heck could be causing this? As stated previously, it never did this before I took it in for body work. It maybe coincidental, but I'm just throwing that out.
SInce diesels use compression and heat to ignite the fuel, my guess a cylinder is still cold enough to not properly ignite/burn the fuel. Sure at idle its seems to be running ok, but as soon as you give it more throttle(more fuel) its not able to properly burn the fuel.
My dad has an old Cat diesel freightliner that sounds like its missing when cold, but only when you step on the throttle. Idling a bit longer fixes the issue.