A cylinder valve control stem for a vehicle drivetrain including a transmission and an engine having a variable valve control mechanism which can vary valve lift diagram in response to a control signal. A controller develops the control signal in response to varying operating condition of the engine. The controller derives, upon initiation of a shift in the transmission, engine speed to be established after completion of the shift and corrects the control signal such that the variable valve control mechanism provides one of various valve lift diagrams whose predetermined value in engine speed is not exceeded by the derived engine speed.