Best first step is to scope the problem. USB borescopes are pretty decent nowadays, and very affordable. You could just go in with cleaner, but if there is indeed masses of carbon present, you could break chunks of carbon off and end up killing the turbos. Ford generslly has done a better job of keeping the coking down in GTDI engines, but 140k can still be a challenge.
Seafoam is probably ok, it is not a harsh cleaner, There are now professional strength cleaners available ftom BG and Valvoline among others that will work better, but again first step. .. scope. glock-coma has done this before, hope he chimes in.