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.
Check Engine Light Due to Intake Manifold Vacuum Leaks on Cadillac Seville SLS
Average mileage: 111,600 (59,000–143,000)
18 people reported this problem
2003 Cadillac Seville SLS 59,000 mi, Visitor
intake boot cracked due to bad front motor mounts
2001 Cadillac Seville SLS 143,000 mi, Visitor
Found a hose was not plugged in, plugged it back in. Error code went away in about 10 seconds.