My wife's 2013 C-max has been problem free since we bought it in March 2014. Recently, however, she noticed a bit of excess vibration or "shuddering" when the ICE was on for the first 5-10 minutes of her journey. I suspected transmission or linkage problems, but after taking the car into our local dealership, apparently the transmission is fine and the problem is carbon build-up. Ford is recommending a "terra clean".
I have a fair bit of experience tinkering with 60's-70's era cars, but this is beyond my scope of knowledge. Does it sound reasonable that carbon build-up could cause initial excess vibration, but then the car runs perfectly after that? I have to admit I'm skeptical.