The evolution in velocity and configuration spaces of ions injected into a flowing turbulent magnetoplasma is studied from a test particle viewpoint. Numerical integration of the equations of motion for several types of fluctuations and injection velocities permits assessing the effectiveness of the turbulence in forcing the ensemble average velocity of the ions to approach the bulk flow velocity. The choice of parameters models the geomagnetosheath, and the downstream ions eventually decoupled from the solar wind flow while crossing the bow shock, but the envisaged conditions are relevant to several space plasma situations. The observed power spectra of the fluctuations in the sheath suggest that, though infrequently, the coupling of the injected ions to the bulk plasma motion may be attained within a few gyroperiods, strongly modifying the dynamics imposed by the average magnetic and convection electric fields.