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My 2001 a4 started knocking on the top end of the motor but only at a stopped idle and starting throwing these codes
P0171
P0011
One was for my can sensor and one sAys bank one is too lean,
Clean your mass air flow sensor and check your fuel trim numbers using a VCDS (VAG-COM). You may have an unmetered air leak or a bad MAFS (been there ... done that with my 2001 Passat).