In recent years, carbon deposits on the intake valves of GDI engines have been a growing problem because the intake valves run dry in these engines. Consequently, there is no direct fuel spray from the injectors to keep them clean — so fuel tank additives do little or nothing to keep the valves clean in these engines.
There are aerosol maintenance products that are specially formulated to deal with each of these issues. Some products contain special cleaners that can remove surface contaminants from MAP sensors (electronics cleaner or MAP cleaner, for example). Other types of cleaners should not be used on MAP sensors because the chemicals may be too harsh or leave behind residues that would affect the operation of the sensor.
Dirty carburetors and throttle bodies can be cleaned with products that are formulated for this purpose. Liquid fuel additives that are added to the fuel tank are best for cleaning the internal passages in a carburetor and for cleaning dirty fuel injectors.
Carbon deposits on valves and in combustion chambers usually require a product that is poured or sprayed into the intake manifold, or fed in through a vacuum hose while the engine is idling. Again, there are specially formulated products for cleaning the valves on GDI engines as well as products for removing stubborn carbon deposits from combustion chambers and pistons.
The bottom line is read the product label and usage recommendations on the product. Equally important is to follow the usage instructions and precautions on the product. Many have been reformulated to make them more environmentally friendly. Even so, if a product says to use in a well-ventilated area, you can assume the fumes should be avoided.