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2000 Ford Crown Victoria P71 - OBD2 Codes P0174 and P0171, Rough Idle After Start, MAF and EGR Replacement

Model: 2000 Crown Victoria Fault Code: P0171 Posted: 2006-05-11 19:10

I own a 2000 Ford Crown Victoria P71 with 60,800 miles. Previously used as a marked cruiser, it's now deployed as an EMS 'fly car' for rapid response. While driving to an emergency call, I accelerated hard and three seconds later the engine died completely. The vehicle was towed to a mechanic. Initially, he suggested replacing the fuel pump, but after retrieving diagnostic codes, he replaced the Mass Air Flow (MAF) sensor located by the air filter. After this replacement, the car started normally. He then claimed that the Exhaust Gas Recirculation (EGR) system was involved and replaced the EGR valve as well. The next morning, the engine started fine but ran roughly when cold—improving once warmed up, though still showing a slight roughness. This pattern repeated on two subsequent days. On one afternoon, I noticed a Check Engine Light (CEL) illuminated with code P0174. I returned to the mechanic, who recommended replacing both left-side (Bank 2) oxygen sensors, estimating the cost at $335. I have since cleared the codes. The MAF sensor is now new and I’ve not cleaned it. I haven’t found any visible vacuum leaks—though I’m unsure if I'm inspecting the correct areas. Currently, I am also receiving P0171 (Rich mixture in Bank 2). The mechanic suggested using a fuel additive such as catalytic converter cleaner. However, I’m skeptical about its effectiveness for these specific misfire and air-fuel ratio codes. Any insights or troubleshooting steps would be greatly appreciated. — Mike

Related fault codes
P0171P0174
Comments (3)
Anonymous 2006-05-12 00:09

Check for vacuum leaks in the intake system, particularly at the intake manifold, intake gaskets, and all connected hoses. Use brake cleaner or a similar spray to test potential leak points—apply around seals and connections while the engine is running. A vacuum leak can cause both P0171 and P0174 codes on Ford Crown Victoria models. Also inspect PCV (Positive Crankcase Ventilation) lines for cracks and ensure the PCV valve is functioning properly. This issue is common in older Ford vehicles with these specific OBD2 codes. When was the last time your fuel filter was replaced?

Anonymous 2006-05-12 06:06

The fuel filter was replaced less than 1,000 miles ago.

Anonymous 2006-05-17 16:27

OK, follow-up: I discovered a vacuum leak near the newly installed EGR valve. The gasket wasn’t properly seated during installation, which likely caused both P0171 and P0174 codes. Reinstalling the EGR with proper sealing resolved the issue.