In this paper we consider how the boundary-layer flow induced by a constant temperature vertical surface embedded in a porous medium is modified by time periodic variations in the gravitational acceleration. It is assumed that the amplitude of these variations is comparable with the mean gravitational acceleration. The resulting nonsimilar boundary layer equations are solved using the Keller-box method after using a Fourier decomposition in time to reduce the system to parabolic form with only two independent variables. The main effect of such g-jitter is confined mainly to the region near the leading edge and becomes weak at larger distances from the leading edge. For small g-jitter amplitudes the numerical results compare very well indeed with our earlier analysis in Rees and Pop [Inf. Comm. Heat Mass Transfer 27 (2000) 415].