Refrigerator manufactures claim they have odor testing procedures in place before a refrigerator is shipped. Plastic odor when new is normal and will dissipate with use. The one mechanical part that has been known to cause an odor similar to rotten eggs is the evaporator fan motor. Cleaning the inside walls and shelves of your refrigerator manufactures recommend baking soda and water. Listed below are several odor causing possibilities.
-Food not wrapped
-Spills on shelves
-Evaporator fan motor
Getting rid of the odor sometimes is difficult, plastic over time can absorb the smell. Using chemicals on the walls of your refrigerator may cause cracking or discoloration and is not recommended.
Several things you can try if you have not already are listed below.
-Cleaning drain pan
Vanilla will eliminate odors, vanilla will freeze so only use in the fresh food compartment. Small critters crawl behind refrigerators and can leave droppings and also die. Small critters can get stuck in the condenser fan motor, dieing as a result, when this happens you may notice the center and door seals of your cabinet are warm or hot to the touch. Cleaning the drain pan where the water from the defrost cycle runs down to and evaporates may also eliminate a odor.
As you already know coffee is a great odor eliminator a small bowl of coffee left in for several weeks will also aid in the odor removal.