Flow modulator for a fluid like combustion gas, comprising: a modulator body having a channel providing a flow passage for the fluid; a valve body having an opening providing another flow passage for the fluid; an actuator by which the valve body is rotatably displaceable relative to the modulator body to modulate the fluid flow by changing the overlap between the opening or flow passage of the valve body and the channel or flow passage of the modulator body ; a gear transmission , wherein an input side of the gear transmission is in operative connection with the actuator having a fixed axis of rotation , wherein an output side of the gear transmission is in operative connection with the valve body having a translationally displaceable axis of rotation , and wherein the valve body has a guide pin being positioned in the axis of rotation of the valve body , characterised in that the modulator body has a guide groove for the guide pin of the valve body , wherein the guide groove is configured to allow a rotational displacement of the valve body relative to the modulator body , allow a translational displacement of the valve body relative to the modulator body in a distance direction (X) of the axis of rotation of the actuator and the axis of rotation of the valve body , prevent a translational displacement of the valve body relative to the modulator body diagonal and/or orthogonal to said distance direction (X) of the axis of rotation of the actuator and the axis of rotation of the valve body . a modulator body having a channel providing a flow passage for the fluid; a valve body having an opening providing another flow passage for the fluid; an actuator by which the valve body is rotatably displaceable relative to the modulator body to modulate the fluid flow by changing the overlap between the opening or flow passage of the valve body and the channel or flow passage of the modulator body ; a gear transmission , wherein an input side of the gear transmission is in operative connection with the actuator having a fixed axis of rotation , wherein an output side of the gear transmission is in operative connection with the valve body having a translationally displaceable axis of rotation , and wherein the valve body has a guide pin being positioned in the axis of rotation of the valve body , characterised in that the modulator body has a guide groove for the guide pin of the valve body , wherein the guide groove is configured to allow a rotational displacement of the valve body relative to the modulator body , allow a translational displacement of the valve body relative to the modulator body in a distance direction (X) of the axis of rotation of the actuator and the axis of rotation of the valve body , prevent a translational displacement of the valve body relative to the modulator body diagonal and/or orthogonal to said distance direction (X) of the axis of rotation of the actuator and the axis of rotation of the valve body . allow a rotational displacement of the valve body relative to the modulator body , allow a translational displacement of the valve body relative to the modulator body in a distance direction (X) of the axis of rotation of the actuator and the axis of rotation of the valve body , prevent a translational displacement of the valve body relative to the modulator body diagonal and/or orthogonal to said distance direction (X) of the axis of rotation of the actuator and the axis of rotation of the valve body . <EOS>