US Patent 10330035 Method and system for determining air-fuel imbalance

Methods and systems are provided to determine air-fuel imbalance of cylinders in a variable displacement engine. In one example, the method may include during a cylinder deactivation event, sequentially deactivating each cylinder of a cylinder group including two or more cylinders and estimating a lambda deviation for each cylinder following the sequential deactivation of each cylinder of the cylinder group; and learning an air error for each cylinder based on the estimated lambda deviation.