Hi. Thanks for the query.. Foul taste in mouth that is more prominent on coughing can be due to respiratory tract infection, sinus infection, acid reflux, oral and throat infections etc.. So my suggestion is to first of all consult an Oral Physician or an ENT Physician and get evaluated, so that a clinical examination can be done. Further investigations can be advised as per the suspected cause.. For now you can chew flavoured sugarfree chewing gum, gargle with flavoured antiseptic mouthwash and do warm saline gargles.. You can also do steam inhalation by putting a few drops of Eucalyptus oil in boiling water. It will help in freshening your breath.. Avoid high aroma foods like onion and garlic.. Hope this helps.. Regards.