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ive got a 00 zts and the other day my c.e.l. came on so i drove to oreillys and had them hook up there diag. equip. and p0171 came up,engine running lean bank 1. when the car is in motion there is no hesitation or jerking,however, when the car is at idle the eng. bogs down a couple hundred rpms and comes back to normal idle rpm.it does this sporadically. i know this code can mean a multitude of diff. problems but im really thinking its either a vacuum leak or a 02 sensor has gone bad.can you fellas offer any advice on what to look for
 

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more than likely you have a vacuum leak. the o2 sensor is fine its doing its job and telling you are running lean
 

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In most cases a Vac leak means higher idle , If it shows a lean bank 1 , when the front o2 sensor fails it fails to the lean side , I would get a scan tool and check your front o2

My guess is bad front o2 sensor and if you change it (wouldnt till you confirm its bad) make sure you clear the batt (neg cable off for 4-5 min) or it will take some time for the new o2 to work properly and you will think it wasnt the front o2 and change more parts

Tom
 

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In most cases a Vac leak means higher idle , If it shows a lean bank 1 , when the front o2 sensor fails it fails to the lean side , I would get a scan tool and check your front o2

My guess is bad front o2 sensor and if you change it (wouldnt till you confirm its bad) make sure you clear the batt (neg cable off for 4-5 min) or it will take some time for the new o2 to work properly and you will think it wasnt the front o2 and change more parts

Tom
im confused, im geting conflicting info here and not sure which way to turn
 

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im confused, im geting conflicting info here and not sure which way to turn
It's because we're guessing. Without a data log or looking at the vehicle it's just a guess. The PCV line is a typical problem for a Zetec or any vehicle that's 10+ years old. It could be other lines, but that one is the one that people on this site have the most trouble with. The elbows can decay and collapse, or leak causing idle and engine running issues. Ford makes a replacement, or you can piece together plastic elbows and hose from an auto parts store. There might even be an aftermarket molded hose available. If it has insulation on it- that's even better. The Ford part does so that excess heat doesn't cause the rubber to decay prematurely. If you want to test it to be sure that you're replacing the correct part, then unplug the PCV vacuum line, then plug the hole with a cap. If the car starts running right- then you're on the right path.

Replace the PCV itself while you're at it- it's inexpensive.

O2 sensors cost about $100- always get the OEM style that just plugs right in. Never get Bosch. Everyone on this site has had problems with those parts. Any O2 sensor older than 100k miles is suspect to be bad, so perform whatever kind of test you can on it- if you can test it. If you don't know anyone with an SCT XCal that you can get a data-log with, then you might just have to replace the part, cross your fingers, and hope that's it. Other typical O2 sensor woes are bad fuel economy. I have a bad one right now and my mpg has dropped to 26 on a drive that typically gets me 30ish.
 
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