An electric power wrench for fastening and loosening joints includes: a main shaft for delivering a torque to a joint, an electric motor that is arranged to selectively drive the main shaft in two opposed rotational directions, a control unit for controlling the drive of the electric motor, and a transmission that connects the electric motor to the main shaft. The control unit has a first drive mode in which it controls the electric motor such that it delivers a continuous torque in a forward direction, and delivers torque pulses in an opposite backward direction, wherein the transmission includes an inherent play and wherein the torque pulses are produced in said play.