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P0171, P0174, and P0304 Faults in 2000 Lincoln LS V6: Causes and Fixes

Model: Lincoln LS V6 Fault Code: P0171 Posted: 2006-01-14 18:53

I own a 2000 Lincoln LS with a V6 engine that has been running roughly for some time, and the service engine light has remained on. After retrieving diagnostic codes, I found P0171 (Rich mixture in bank 1), P0174 (Rich mixture in bank 2), and P0304 (misfire detected in cylinder 4). My question is: could the misfire code P0304 be caused by the fuel trim issues indicated by P0171 and P0174? Where should I begin troubleshooting? I’ve considered replacing the mass air flow (MAF) sensor, but I’m aware that inspecting spark plugs and coils on this model requires removing the intake manifold—a complex task. What are the most effective steps to diagnose and resolve these issues?

Related fault codes
P0171P0174P0304
Comments (5)
Anonymous 2006-01-17 11:42

I discovered that the air intake housing was not properly seated near the air filter. The oil change shop failed to reseat it after replacing the air filter. I replaced the spark plug coil for cylinder #4 and have since eliminated the P0304 misfire code. The engine now runs smoothly. I cleaned the MAF sensor and added a fuel injection cleaner. Currently, no diagnostic codes appear when running in the garage at 2000 RPM for 10 minutes. However, during idle after warm-up, it initially idles between 1000–1100 RPM before dropping to 800–900 RPM and then stalling. I replaced the fuel filter about one to two months ago. Any suggestions on resolving the stalling issue? I plan to drive it for an hour during lunch to see if any codes return. Does anyone have advice?

Anonymous 2006-01-17 15:57

I drove approximately 60 miles at lunch and am still seeing P0171 and P0174 codes. The idle stalling issue persists. Anyone else experiencing this? Any recommendations for a fix?

Anonymous 2006-01-18 15:02

No diagnostic codes are appearing after today’s drive. I believe the fuel injection cleaner may have resolved the issue. This forum is extremely unhelpful—there's zero meaningful responses or guidance available.

Anonymous 2006-03-20 19:23

No codes appear after today’s drive. The fuel injection cleaner likely helped resolve the problem. This site offers little value for users seeking real solutions. If you're criticizing the community without offering constructive input, it's hard to get useful advice. I suspect a vacuum leak beneath the intake manifold—this is a common issue on the 2000 Lincoln LS. The PCV hose runs underneath the manifold and is prone to splitting or leaking. I found this insight from a reliable diagnostic resource at http://d-tips.com. This could be a key factor in both misfires and fuel trim issues. If you're under 7 years old or 70,000 miles, many dealerships may offer free repairs due to manufacturer emission system warranty requirements. Warranty terms vary by model year and vehicle.

Anonymous 2006-03-21 10:50

The 2000 Lincoln LS frequently suffers from vacuum leaks under the intake manifold. The PCV hose, which runs beneath the manifold, is especially susceptible to cracking or leaking. This can cause misfires (like P0304) and abnormal fuel trim readings (P0171/P0174). I found this troubleshooting tip on a dedicated diagnostic site: http://d-tips.com. This insight may help others diagnose similar issues.