To keep things simple, the answer is yes! However, they cannot do all the work by themselves. Maintaining your engine does not involve using only cleaners. Changing the fuel filter, using premium gasoline with the appropriate octane rating for your vehicle, and also high-quality fuel additives are all key factors to a smooth running engine.
When added to fuel, these concentrated cleaners pass through the carburetor and injectors and loosen and remove accumulated varnish deposits. These sediments are burned up through engine combustion and the result is a noticeable difference in idle smoothness, emissions, as well as fuel economy.