Gasoline vapor deposits left in fuel injector nozzles after an engine is shut down form hard varnish. Over time, it can build up and clog the injectors. Gasoline additives and detergents already mixed into the gasoline you buy help reduce this problem, but they can’t eliminate it entirely. Injectors periodically need to be cleaned. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency.
But first, a word on prevention. In the U.S., most of those generic gas stations with names you’ve never heard of purchase their gasoline from the lest expensive source, sometimes including refiners who, to save a few pennies, may skimp on the engine-protecting detergents added to their product; name brand gasoline filling stations on the other hand are more reliable, many use their ‘special’ additive cocktail in their sales pitches.