Throttle loss recovery (TLR) systems for a spark-ignition engine are described having a turbine (either variable or non-variable) that expands incoming engine air and drives an electrical generator. A bypass passage and bypass valve can allow air to bypass the turbine under certain operating conditions. Control algorithms are employed for controlling the generator load and the valving of the TLR system, such that the generator serves an electrical load only when it is efficient to do so, in particular, only when the generator speed is above a predetermined minimum speed threshold. The control methods also aim to prevent any overspeed excursions of the turbine/generator assembly. In some embodiments there is also a series throttle valve arranged upstream or downstream of the turbine. The control methods include various algorithms for controlling the bypass valve, the VNT (when present), and the throttle valve (when present) under various engine operating conditions and scenarios.