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.Google+
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