I have a 2010 Tiguan Wolfsburg Edition, purchased pre owned from VW with 5k miles on it. At 20k miles the "intake manifold runner assy to be faulty" was replaced. I now have 42k miles and have been experiencing sluggish exceleration and running until the car warms up. I took it in and was diagnosed to have a "cold start misfire on 3 cylinders". Upon examination with a borescope excessive oily carbon build up on intake valves were found. This is hard to swallow considering this car has 42k miles on it and I always use premium fuel. Does this seem normal or acceptable???