Identification and suppression of asymmetric errors

Methods and systems for identifying and suppressing asymmetric errors that cause engine emissions are shifted to the rich or lean, is provided. In one example, a method for an engine system comprising generating a UEGO sensor feedback set point adjustment on the basis of slower and faster time components within an outer loop of a catalyst control system, generating a displacement-offset correction of the inner loop based on the slower time component and indicating the deterioration of the internal combustion engine system to based on a comparison of the displacement offset correction with a deterioration threshold. In this way, the total control authority of the outer loop is increased, while the driveability and noise, vibration, and roughness (NVH) marginal conditions are maintained, and emission standards are met in the presence of an air-fuel ratio shift error.