Subaru sells a cleaning tool kit and a couple of different cleaners to be introduced through a vacuum hose, I'm hoping to try one of the cleaners this weekend (I bought both types, top engine cleaner and carbon clean). I tried introducing a CRC spray cleaner through the open airbox and that didn't go so well, ended up having to clean my MAF sensor and I suspect that the cleaner pooled up somewhere based on the way my car acted just after the process. The nozzle of the spray can was past the MAF, but I think there must have been some backspray. My car did run incredibly well after I cleaned the MAF, though, but I don't now if it was from the valves getting cleaned or me getting already existing gunk off the MAF (or just completely my imagination).