With all the posts regarding ignition misfires, coil pack failures and plug problems it seems the oil companies are trying to help with a new reformulation and classification (SN plus or SN +).Our small displacement GTDI engines seem most susceptible. Haven't seen any of the 5W-40 weights reformulated yet but many already add the classification to the 5W-30 oils. I will be changing to it on my new '20 N-line @ 1000 miles.
I know most GDI motors are subject to carbon buildup on valves because port injectors used to keep them clean. I know some manufactures have both now to get rid of that problem. Frequent oil changes and catch cans are supposed to help.