The effects of high and low frequency excitation, on nominally 2D flow properties of a turbulent boundary layer under strong adverse pressure gradient, without the complicating presence of curvature, was analyzed in both experiment and by CFD. The adverse pressure gradient was produced using suction velocity from the wall opposite to the flat test plate. The effect of different suction levels on the turbulent boundary layer pressure distributions and velocity profiles were measured by several techniques, including particle image velocimetry. The effect of the excitation on the turbulent boundary layer was studied, both in experiment and also using the commercial CFD code FLUENT. The vortices generated by the actuator, their interaction and effect on the separating shear layer were all quantified.