Lean operating hybrid gasoline engine

An engine control unit (400, Fig 5) for a full hybrid engine 100 with an internal combustion engine 110 and an electric motor 120 is configured to operate the internal combustion engine in a lean-burn mode, to determine a current load level of the full hybrid engine and to compare the current load level to a lean-burn load threshold (210, Fig 3). The lean-burn load threshold defines a load level below which stable operation of the internal combustion engine in the lean-burn mode is impossible and/or undesirable. If the current load level of the full hybrid engine is below the lean-burn load threshold, the internal combustion engine is decoupled from the drivetrain and the full hybrid engine is operated in an electric mode. The engine control unit preferably determines a current RPM of the full hybrid engine and to determine the lean-burn load threshold in dependence on the current RPM, or a current NOx concentration in an exhaust stream of the internal combustion engine, while the internal combustion engine is operating in the lean-burn mode. An internal combustion engine, a full hybrid engine, a powertrain for a vehicle, a vehicle and method of operation are also claimed.