Remove the tray from inside the microwave and wash it with warm soapy water.
Unplug the microwave.
Mix 2 tbsp. liquid dish detergent and ¼ cup of chlorine bleach into 1 qt. of warm water and wipe down the inside of the microwave with it. Use a small brush to clean inside the door seal and other hard to reach areas.
Mix 2 tbsp. baking soda into 1 cup of warm water and use the solution with a clean cloth or sponge to rinse the inside of the microwave.
Wipe the microwave dry with a towel and leave the door open for 30 minutes to allow it to finish air drying.
Place the clean tray back into the microwave and plug it back in.
Add 1/2 cup lemon juice to a microwave-safe cup of water and place it into the microwave. Heat this solution for five minutes.
Wipe down the inside of the microwave with a clean dry towel to remove any residual moisture that may have overflowed from the cup.
Reheat the cup of lemon juice and water for another five minutes if the odor is still there.