A tamper resistant hydrocarbon trap and air filter assembly includes a cylindrical carbon trap filter extending from a sealed upstream end to a downstream end seated and sealed in a forwardly facing recess of an adaptor. A conventional cylindrical air filter surrounds the carbon trap filter with a sealed upstream end and a downstream end removable secured to an annular flange on the adaptor with the downstream end of the adaptor being arranged to be coupled to a vehicle's air intake.