An intake manifold vacuum leak can develop from a variety of sources, often causing illumination of the Check Engine Light with codes P0171 & P0174 stored. Thorough diagnoses will be necessary to pinpoint the cause in order to make the correct repairs. A "smoke" machine is often used to isolate the cause of difficult to find vacuum leaks.
Car Problem Reports
Cadillac DeVille Check Engine Light Due to Intake Manifold Vacuum Leaks
Cadillac DeVille Problem
Engines Affected: 4.6L V8, 4.9L V8
Average Mileage: 122,425 mi (11,700 mi - 187,000 mi)