2003 Cadillac Deville P0174 - Engine Misfires and Idle Issues After Plug Replacement
During a recent 100-mile round trip at approximately 60 mph, my 2003 Cadillac Deville began experiencing severe idle misfiring, nearly stalling at low speeds. I checked the diagnostic trouble codes and found P0101, P0300, P0171, and P01704. After replacing the front four spark plugs (due to time constraints, not all were replaced), the codes have reduced to only P0174 after about 20 miles of driving. I'm concerned this issue may stem from a deeper intake system problem. Any insights or suggestions on how to diagnose and fix this specific code in my 2003 Deville?
Inspect the rubber boot connecting the intake manifold to the throttle body—this is NOT the air duct from the air filter. Follow the intake pipe from right to left: you'll see a rubber coupler, followed by a metal spacer, and then the throttle body. This boot can crack or split over time, leading to vacuum leaks that cause misfires and trigger P0174. With the engine running, use carburetor cleaner to spray around the boot; if the engine stumbles or hesitates, it confirms a leak. This is a common issue in 2003 Cadillac Devilles and should be checked thoroughly.