AIR ADMITTANCE VALVE BAD ODOR:

AIR ADMITTANCE VALVE PROBLEMS WITH THE PIPE IN MY KITCHEN, IT IS CLOGGED THERE IS LEAKING AND BAD ODOR IN THE PLUMBING 

Air admittance valve can have bad odor, when a horizontal section of the venting system connecting to the air admittance valve is sloped too much the wrong way.  The air admittance valve itself becomes smelly and the bad odor issue.  It will need to be removed and replaced.  Not recomending cleaning an air admittance valve because you never know if you got it fully cleared out or not.