This paper describes both an analysis and a practical method to suppress periodic oscillations of both unloaded and extremely light-loaded engine revolutions. A frequency-domain analysis based upon the transfer functions is proposed and analyzed by identifying the parameters which appear in the transfer functions. As the results of the proposed analysis, the following results are obtained: (1) Both the unloaded and extremely light-loaded oscillations are caused by the self-exciting oscillations of the closed loop in the idling engine system. (2) A rough standard for the determination of the manifold volume was obtained. (3) The derivative fuel modulation is most practical as the suppression method of the oscillation.