Check the air filter, spark plugs, and fuel pressure. Inspect for a clogged fuel filter and an overworked fuel pump, clean the fuel injectors if needed, and check the idle air control valve, mass air flow sensor, and oxygen sensors.
The owner of a Nissan truck said it failed a smog test for using too much fuel after passing for two years. An expert recommended checking the air filter, spark plugs, fuel pressure, fuel filter, fuel injectors, idle air control, mass air flow sensor, and oxygen sensors, noting that fuel use depends on spark and oxygen.
