The invention relates to a method for producing a plastic part, especially a plastic part for an automobile, by an injection molding method comprising the steps: Using an injection molding device, plastic in a flowable state is injected into the mold cavity of an injection mold, gas under pressure is injected through a gas inlet opening in the injection mold into the mold cavity of the injection mold by means of a gas injection device so that a gas bubble forms within the still flowable plastic, the plastic is heated and kept flowable, at least in a region neighboring the gas inlet opening while the plastic is hardening in the mold cavity, wherein pressure is exerted on the plastic being kept flowable so that an opening in the plastic in the region of the gas inlet opening is sealed, and the plastic part is removed from the injection mold after reaching a sufficient dimensional stability. In addition, the invention relates to a corresponding device.