while receiving first feedback from a vibration sensor coupled to a first cylinder of the engine, perturbing the first cylinder during engine operation;

responsive to the first feedback indicating a first vibration level difference greater than or equal to a first threshold difference, setting a first indication of a first degradation condition of the first cylinder; and

thereafter

operating the engine based on whether or not the first indication was set,

wherein perturbing the first cylinder comprises:

actively perturbing the first cylinder by cutting out fuel to the first cylinder; and

responsive to the active perturbation of the first cylinder, passively perturbing each second cylinder of a plurality of remaining cylinders of the engine by redistributing an engine load among the plurality of remaining cylinders, wherein the plurality of remaining cylinders includes all cylinders in the engine excepting the first cylinder.