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 Seville SLS Check Engine Light Due to Intake Manifold Vacuum Leaks
Cadillac Seville SLS Problem
Average Mileage: 131,000 mi (119,000 mi - 143,000 mi)
Visitor, 2001 Cadillac Seville SLS, 143,000 mi
Found a hose was not plugged in, plugged it back in. Error code went away in about 10 seconds.
P0101, P0300, P0131, P0171, P0174