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I have a 2000 Mercury Mystique with a 2.0 engine that had a check engine light appear a few days ago. I had a friend check it and code P0171 appeared. He cleared it and it didn't appear until 2 days later and I then stopped at my local AutoZone and it was definitely the same code (P0171). I asked the guy what he thought and the first thing out of his mouth was "bad 02 sensor on Bank 1". Not knowing which sensor is Bank 1, I decided to purchase 2 new 02 sensors (because the Mystique takes 2). Unfortunately, the only 02 sensor that I could get out was the one near the catalytic converter. The one near the exhaust manifold would have to wait until my brother (the true mechanic) can remove that one.

Then I decided while I had the car up on ramps that I would change the oil and when I was changing the air filter, I noticed a small deposit of oil in the bottom of the air filter housing and the crankcase breather filter was saturated with oil. I went to the local Ford dealer and purchased a new CBF. Then, I pulled the spark plug wires to check the condition of the plugs and was surprisingly met with a decent amount of oil in the holes where the spark plugs sit. What confuses me is that I don't see any oil leaking on the exterior of the valve cover gasket and maybe the grommets on the inside are shot and that's why the oil is leaking near the spark plugs. The car is NOT blowing BLUE smoke in case you're wondering.

I assumed the following conditions and maybe someone could correct me if I'm wrong.......

a) 02 sensor above the exhaust manifold needs to be replaced; and
b) the PCV valve needs to be replaced; and
c) I need to install a new valve cover gasket.

Can anyone point me in the correct direction as to what I'm looking for?  

P0171 is a lean code...not O2 code...FYI parts guys are not techs..the 2.5L v6s have problems with plenum gasket vaccume leaks...have you checked for vaccume leaks?

Nick
ASE Master Auto Technician, L1  
ASE Master Auto Technician, L1, ASE Certified Service Consultant, ASE Certified Parts Specialist, Chrysler Certified Service Manager/Technician