Carbon cleaning. Not terraclean method. Intake method instead.

[ainarssems]

I would like to see results of this if somebody was willing to take manifold off to inspect, put it back, go for hydrogen cleaning then take manifold off and inspect again to see the difference.

My suspicions are that there is no wonder solution that will undo 10 years of buildup in 45 minutes without mechanical cleaning. If you used it twice a year since new maybe it would make a difference but would be a lot of money spent over time.

Some engines have twin injection, maybe that's the way forward or a retrofitting option. You could put one small injector in manifold inlet spraying in small amount of fuel in as you drive along to keep it clean.

The EA888 engines are a family of four cylinder engines that are currently in use across the Volkswagen Group. The EA888 family is an Audi-designed unit that features some of the latest engine technology such as direct fuel injection, sintered camshaft lobes, thin-walled engine block, variable valve timing and lift for intake and exhaust valves, downstream oxygen sensors, turbocharger integrated into cylinder head, exhaust gas recirculation and cooling, distributorless coil-on-plug ignition, lightweight engine internals, slide valve thermostat (some variants), and the addition of port fuel injection to aid low load fuel consumption and cold start emissions. The port fuel injection also aides in reducing the potential carbon deposits that can occur in direct injected engines. As of 2016, the 'dual injection' system has not been offered in North American markets. Still, Volkswagen has made numerous enhancements to their engine designs such as the positive crankcase ventilation, repositioning injectors and more to lessen the potential that carbon deposits accumulate on intake valves. Currently, the EA888 engine is available in two sizes: 1.8T and 2.0T. Engine output ranges from 111 kilowatts (151 PS; 149 bhp) to over 223 kilowatts (303 PS; 299 bhp). A concept car based on the Volkswagen Golf R, dubbed R400, produced over 400 hp from 2 litres of displacement. If produced, the R400 would hold the record for highest output/litre of displacement for any currently produced inline four cylinder, beating the Mercedes-AMG A45/CLA45/GLA45 which currently holds the record.