Fuel Injectors are located in the Intake Manifold. They provide a precise atomized mist of fuel at exactly the right moment for optimized combustion. Fuel Injectors are very susceptible to deposits that restrict the fuel flow and spray pattern. Most fuel injector deposits form after the vehicle is shut of and the last drop of fuel evaporates on the tip of the injector. This is why cars that are driven on longer commutes can go longer distances between injector cleanings.
The intake manifold supplies the engine with metered air to mix with the fuel provided by the Fuel Injectors. Inert gasses (exhaust gas) provided by the EGR (Exhaust Gas Recerculation) Valve are injected here also. The intake manifold is susceptable to deposits from EGR gasses and PCV (Positive Crankcase Ventilation) gasses. Long distance and short distances drivers are equally susceptible to the formation of deposits in the intake manifold. Induction system cleanings are required to maintain maximum performance.