If the code set at idle, positive fuel trim, check for vacuum leak and check maf system. Some ford makes and models, with everything off, disconnect the maf sensor, where applicable. Take the vehicle for a spin, if it is better, check the maf system. My US database didn't show escort in this model year. Is this vehicle sold in the US?
SOURCE: 2000 ford escort ZX2 with P0171 trouble code.
I am working on the same problem. This 2000 ZX2 was idling rough and throwing a p171 code (bank 1 too lean). I hooked up a scanner to the OBDII port and you could see the O2 sensor at 0 or very low voltage and not switching and the fuel compensation maxed out which indicates a lean condition. Using a flammable Carb cleaner and the engine running I sprayed around the vacuum hoses until the idle picked up. I found a rubber elbow that connects to the bottom of the intake maniflold and feeds vacuum to the PCV valve. Replacing the the elbow with a suitable replacment from the auto part misc parts cards display had it running smoothly and the O2 sensor switching properly. Since this was happening at idle it was not the fuel filter which can cause a lean condition in upper rpms. It is not the MAF or the O2 sensor since it switches when not at idle. Also check the smaller vacuum lines that go to the evap control from the intake vacuum ports (back of manifold just below the throttlebody, most will be cracking if your car is anything like mine. I have also seen this problem with a bad PCV valve.
SOURCE: 2000 Toyota tacoma with code P0171.
You don't say if it is a 4 cyl or 6 cyl engine.
The code means the O2 sensor is telling the computer the engine fuel mixture is too lean and the computer can not make the injectors provide enough extra fuel to make the sensor go rich.
Reasons can be a faulty cooling thermostat, low fuel pressure, vac leaks, exhaust leaks, and other engine problems.
http://engine-codes.com/p0171_ford.htmlForum CodePossible causes- Intake air leaks177 views
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