If a bathroom toilet odor cannot be found, there may be a gap between the wax ring and the toilet base.
A toilet rocking, sewer smell or toilet movement is probably the need for a toilet wax ring repair. The wax ring sealing the toilet to the floor is not expandable. Once it is crushed it does not spring back; thus we know there is a small gap between the toilet and the closet flange.
A rocking toilet may only leak a small amount of air, sewer gas, but in a bathroom it will seem like a lot. Besides the air, it will leak a few drops of water each flush, and even though it is not obvious, it is causing floor damage because the trapped water evaporates slower.
Remove the toilet and clean the floor and old wax off the closet ring. Then take the toilet without a wax ring and place it over the floor flange with the bolts in place. Rock the toilet back and forth and side-to-side with a level to determine which direction would make the top of the toilet bowl level. Insert shims between the toilet and the floor so it is stable.
Once the toilet shims are in place tape them to the floor so they do not move during installation. Place the new wax ring on the toilet and install it on the flange. When installing a toilet bowl over the flange, expect the wax ring to make contact with the toilet bowl about one-quarter-inch before the bowl hits the floor. You may need two wax rings to make a good seal, especially if the toilet is shimmed very high.
Use only two fingers on the wrench when tightening the closet bolts. Many a closet flange is broken when too much force is applied. Use your body weight to help crush the wax rings before bolting down a toilet. Remember, a toilet is a china fixture, so take your time.
Trim the shims if they are protruding from under the bowl. Then caulk or grout between the bowl and the floor to finish this job. Use a tub and tile mildew resistant caulk to fill a thin gap between the bowl and the floor.
When shimming a toilet and the gap between the bowl and the floor is larger than 1/8-inch, use tile grout to fill around the base of the bowl. This will dry fast and hard, giving the bowl better support to the floor.