Contour Enthusiasts Group Archives Forums General Troubleshooting CE light and the code P0171

My check engine light came on about 100 miles ago but the car seemed to be running fine. The car has 70K on it and is a 96 zetek. I took it to the zone and had the code pulled giving me "P0171 System Too Lean - Bank No. 1."

I ignored it for a 100 miles or so until it began to idle sporadically. It has almost a rhythmic tone hanging right around 1000 RPMS. When I drive the car it runs fine, just when I let it idle do I encounter this problem. I replaced the oxygen sensor that is located after the cats I believe. It was very easy to get too as it was right under the front of the car. This did nothing to solve my problems however.

Cash is tight for me seeing as school is back in session. I am trying to get my hands on a MAF sensor from a salvage yard and hope that this fixes the problem.

Any help about the cause of this sporadic idle would be great. Thanks.

If you have only one O2 sensor on the Zetec, then you replaced the right thing. If there are 2 O2 sensors, then you actually wanted to replace the one *before* the cat. (I'm more familiar with the v6) You might want to clean the MAF sensor element with a spray of electronics parts cleaner before buying a new MAF. Radio shack sells small cans of the stuff. Just spray it into the little sampling tube to clean the little wire in there. Might also want to check all the intake hoses and connections for leakage.

I have cleaned the MAF a few times with electronic parts cleaner. I suspected that I replaced the wrong O2 sensor. The wiring on the sensor I purchased would only fit into the wiring harness for the O2 sensor that I replaced.

I did however remove the intake resonator, or at least what I believed was the intake resonator. I removed the wheel well cover and removed everything in there (long tube that reached to the back of the wheel well and ended with a cylinder shaped thing and also a smaller "cylinder") leaving only the part which comes through the fender wall from the intake.

The intake resonator shouldn't be a concern. Verify that there are no air leaks from the MAF inward. If the Zetec has pre-cats on the exhaust manifolds like the v6, then the sensor on the top side of the pre-cat is usually what would report a lean condition. I wish I knew the zetec better...

I will hopefully have the money to replace the other O2 sensor soon. Last night I cleaned the MAF and made sure there were no leaks in the intake.

My question now is what could be causing the PCM to report a lean mixture. Would a bad sensor do this and make the car run rough as well? Or are there other things which could be checked upstream that would cause the lean micture? I recently replaced the pcv valve myself, dont know if that could cause a problem. Thanks for the help.