Bank 1 too lean saga continues

[DougMd]

I replaced the maff, and hooked up a universal oxygen sensor, matching the colors as described by the seller. However, the CEL is on again. Any ideas on what to do/check next? The nightmare continues!

[DiS]

Out of curiosity...What was the code of the first CEL in the first place? or did you check the code for the CEL at all?

[DougMd]

Yeah, it is P0171: "The fuel system for bank 1 was too lean."

[DiS]

hmm, how many miles are on the car? Maybe its the CAT itself?

[DougMd]

About 50,000 miles on the car. First I tried to clean the maff and busted the fragile sensor, so I bought a maff from a recycled dealer. When the light came back on, I bought and installed the universal oxygen sensor on the exhaust manifold (the one accessible from beneath the hood), matching the colors up as instructed.

[DiS]

hmmm. Sorry for ignorance but which year protege do you have?

[DougMd]

No problem, I should have stated it before. Year 2000, 1.8 L.

[DiS]

hmm, with 50,000 miles on the car, its kinda doubtful that your CAT went bad. Hmmm, Ill ask few locals around and see what I can find.

[DougMd]

I checked the crimps on the oxygen sensor and it works fine. I guess the problem could be a leak in a hose somewhere? I have no idea what to do next. It runs FINE, so whatever the problem is, it doesn't have a noticeable effect on performance.

[DougMd]

FYI, it was the intake valve gasket, to the tune of $350.