: Code P 0171 showing - 1999 Deville

Harry Yarnell
11-10-13, 11:22 AM
'99 deville.
a code 171 is a lean mixture in the rear bank, but I can't find the cause. Vacuum lines are solid and don't leak. PCV replaced. O2 sensors (all) have been replaced. Manifold bolts tightened.
What an I missing? Manifold gaskets? Anti-backfire door? Code 174 is NOT set.

11-10-13, 11:49 AM
Does the PCV valve fit tightly in the grommet in the rear cam cover?

Harry Yarnell
11-10-13, 12:48 PM
If I recall, it was a snug/slip fit. Will check.
Tommorow I'll pick up a set of intake gaskets, and see if that will help.
As for cleaning the MAF; what gets cleaned? The wire grid? Throttle plate Bore?
Since there's no code P 0174, I'm leaning towards intake gasket.

11-10-13, 09:46 PM
If it's the intake gasket spraying some Brakleen around the base should tell before you go through all that work.

MAF sensors rarely need cleaning and would not set that code. The grid or honeycomb (if that's what you are referring to) is just an air flow straightener.