Mr.Subaru has just posted a video of the DIY carbon build-up maintenance procedure. With his closing comments in mind this looks like it's a fairly simple and straightforward preventative procedure.
Rod H
Another thing to be aware of is that Mr. Subaru's vehicle is the First Generation Crosstrek that uses the Port Fuel Injection system and not the Second Gen (2018+) that uses a Direct Injection system.
Completely different problems separate those two fuel delivery systems.
This system probably works as advertised in the First Generation, but I suspect not so much in the Second Gen.
The Second Generations Direct Injection system leaves the backside of the intake valves vulnerable to carbon build-up, that this type of intake manifold spray cleaner delivery system does not address.
As far as I know, the only proven way to remove this carbon buildup in a DI system is a mechanical cleaning.
You will also notice that the TSB for the carbon cleaning service allows for up to four attempts to clean the carbon out plus two engine oil changes and up to 14+ hours of labor. That's stupid expensive outside of warranty, and in my estimation is of questionable effectiveness in getting the backside of the intake valves clean. Admittedly it should be pretty effective for cleaning the injectors and combustion chamber.
A mechanical cleaning (walnut blasting or equivalent) would be less expensive and much more effective for cleaning the intake valves.
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