Every 40k miles, inspection of the intake valves is very important, and if they are dirty a Walnut Shell Blasting machine can be used to properly clean them.
After this service you can maintain them with an Induction Service. By keeping intake valves clean you can increase fuel efficiency, restore lost power, and avoid costly repairs. Check our this video. This example is actually a BMW tool using ground up walnuts on a 2014 Audi A4 2.0T with only 40,000 miles on it.