Looking for some help with my sons 2015 Jetta SE. He's been experiencing rough idle. He has 80,000 miles. I did the easy thing and put in some plugs (actually it wasn't that easy!). It still idles rough, but drives good. I ran a scan with VCDS, and he has misfire codes on ALL cylinders. Before I spend his money on coil packs, could it be something else if all 4 cylinders are misfiring? Thanks!