Was having some starting issues in -25C weather a few weeks ago, so I replaced the plugs myself (I'm pretty decent with tools). After a few weeks of regular use, the check engine light and an ECS light came on out of nowhere a few minutes after starting and driving at residential speed. Lost the majority of my power, all of my acceleration, and the car ran very rough with terrible fuel economy. I managed to call around and pull some strings to get a mechanic to look at it just before New Years, and he came to the conclusion that cylinders 2 and 4 were misfiring due to failed ignition coils, at the same time. He replaced both faulty coils and all plugs, and Tiguan runs smooth once again, thankfully.