You don't need to clean intake valves on a port-injected gasoline engine using a dedicated valve cleaning solution as they're constantly being washed by the fuel injectors.

It's a different story on both gasoline and diesel direct-injected engines as they lack that constant fuel stream passing by the intake valves and preventing the buildup of carbon deposits that affects most DI engines. This is why intake valve cleaning products such as the CRC line exist.

However, cleaning the entire fuel system via a cleaning agent deposited into the fuel tank can be very effective as it will help dissolve deposits within your fuel injectors and all fuel delivery components leading up to those injectors. This would be more appropriate for your Subaru if it has been neglected as it will help restore injector spray pattern, critical for an effective and complete combustion cycle.

You don't need to clean intake valves on a port-injected gasoline engine using a dedicated valve carbon-removal solution as the valve neck and face are constantly being washed by the fuel injectors. The valve face is the only part of a valve susceptible to carbon buildup on older, indirect/port-injected engines.

It's a different story on both diesel and gasoline direct-injected engines as neither offer a constant fuel stream passing over the intake valves which would otherwise prevent the buildup of carbon deposits. This affects all DI engines without a supplementary port injection system. This is why intake valve cleaning products such as the CRC line exist.

However, cleaning the entire fuel system via a cleaning agent deposited into the fuel tank can be very effective as it will help dissolve deposits within your fuel injectors and all fuel delivery components leading up to those injectors. Products sold as "Fuel System Cleaner" or "Injector Cleaner" would be more appropriate for your Subaru if it has been neglected as it will help restore injector spray pattern, critical for an effective and complete combustion cycle.