What could cause a fecal/mothball taste in back of throat, increased saliva, which is made stronger with sugar intake and fades with no sugar intake?

Bad taste: Have you had your teeth cleaned recently? Dental problems can cause this. So can allergies, post nasal drip, acid reflux, metabolic diseases, and others. See a dentist or your primary care for an exam to find the answer.

Bad taste: Can be from Gastro-Intestinal distress such as ulcers or GERD. can be from infection in the oral or nasal cavities. Can be from change in diet/supplements/medications. Start with both your General Dentist and General Physician to begin the differential diagnostic process. Find out what's wrong first, then choose appropriate doctor directed treatment.