The invention discloses engine friction model adaptation. A hybrid powertrain includes an engine having a crankshaft and a throttle body, and an electric machine having a rotor selectively coupled tothe crankshaft via a disconnect clutch. A transmission of the powertrain includes a torque converter having an impeller fixed to the rotor, a turbine disposed on an input shaft of the transmission, and a bypass clutch configured to selectively transmit torque from the impeller to the turbine. A vehicle controller is programmed to, in response to the bypass clutch being open or slipping and the disconnect clutch being closed, command a throttle position of the throttle body based on an error between measured and estimated speeds of the impeller.