Abstract: A powertrain control method applied to a lean burn engine coupled to a continuously variable transmission for minimizing engine out emissions selects one or more control parameters from a plurality of parameters that may be precisely controlled to provide for acceptable powertrain control with minimized emissions. Lean burn engine operation is maintained under low brake mean effective pressure conditions by modulating powertrain output power through transmission drive ratio variation. Fuel and air per cylinder may further be varied with the drive ratio when low emissions can be provided with minimum sacrifice to fuel economy. Lean burn operation is suspended under high brake mean effective pressure conditions by driving air/fuel ratio toward the stoichiometric ratio to exploit the efficiency of an included three-way catalytic treatment device while lowering engine speed to stabilize combustion.