The possibility of manipulating the electromechanically induced transparency (EIT)-enhanced nonlinearities and the probe light propagation with a pump laser in a four level EIT system were explored. The experimental measurements that demonstrate both slow and superluminal light propagation in cold Rb atoms were presented. It was shown that the light group velocity can be tuned by the pump laser in four-level EIT system. It was also shown that the large nonlinear absorption is associated with the superluminal group velocity. It was suggested that group velocity tuning with the EIT technique may be useful in the optical delay lines and optical data storage applications.