So the car is a 2010 GTI CCTA stratified tuned FBO with APR coils and NGK iridium plugs with about 5k on them. A few months ago, I changed the PCV diaphram with the RKX diaphram. Almost immediately after, the car started misfiring like crazy. Like barely running. So is decided to just change out the complete PCV with a new OEM one from the dealership. But the car was still running the same. Before the diaphram change the car was running fine. So I automatically assumed the main seal is shot and park up the car ( I had shoulder surgery recently and couldnt work on the car on that level ). So fast forward to a few days ago while doing a compression test ( 150 straight across }, I notice the plugs are ridiculously carbon fouled up as shown in the photo below. So i do quick clean on them and reinstall. And what do you know, the car starts right up and is running almost normal. On cold start it misfires a bit but once warm its smooths out and drives fine. Im for sure going to replace the plugs anyway but before i change them I want to know if anyone knows what would have caused this? Im still getting multiple misfire codes after a few starts because the car idles so rough when cold. Im assuming thats because the plugs are still pretty gunky? Since this happened those are the only codes I got, with the exception of a " leak in air intake" code. But i think thats from me not installing the intake to turbo coupler properly. I inspected the plugs again after driving it around a bit and they didnt get any more carbon on them after the quick clean. Thanks in advance for any help. Sorry for the long post.

