Restricted Exhaust
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
To check exhaust system for restrictions, see RESTRICTED EXHAUST under SYMPTOMS in TROUBLE SHOOTING - NO CODES - 4.6L DEVILLE & SEVILLE article.