Without a picture, or knowing the make, model and year, it's impossible to say, but that sounds like it might be the air intake hose. Gasoline engines do need some air taken into the engine in order to fuel the combustion process alongside the liquid fuel.
Air intake hoses are often plastic, so it's easy for them to wrap and even crack with age. This can mean the engine gets dirty inside, and performance and gas mileage suffer. Finding cracks is usually not too difficult, and there are several repair options for those that trust their mechanical abilities. Replacing the air intake hose is also something that can be done DIY or professionally.