In terms of the symptoms of the carbon build-up, typically the noise from the engine contains all the usual tick over noises and fans/pulleys, but is very 'bass-heavy' with a lot of low level rumble, shaking, etc. With the process I'm using this typically disappears within the first 10 minutes and the car idles better. The revs then climb quicker and any flat spots (if carbon related) are eliminated.The rumble is down to the engine struggling, with added friction, reduced 'breathing'. Remove the carbon and the bass notes disappear, the engine works better and as a result you can recover MPG (notice I didn't say gain).
My car does this, have you ever tried this new thing called hydrogen engine cleaner??
Components such as Diesel Particulate Filter (DPF), Exhaust Gas Recirculation Valve (EGR), Turbo and Injectors can all dramatically benefit from the removal of carbon using Green Engine Machine.....they say