I recently had an episode where my 2017 started vibrating and the engine light came on. 20 minutes later I was at my Hyundai dealership and they told me it was a coil pack. That was replaced. However they also told me I needed to have carbon cleaned out of my engine. This surprised me as I only have 30,000 miles on the car and I do highway driving every weekday. I previously had another Elantra for 12 years and it never had a problem with carbon. What I am asking... could the coil pack been bad for some time and I didn't know it and is this what caused the carbon built up? Or have I been taken advantage of ?