Abstract: A vehicle on-board computer method for controlling a diesel engine intake air throttle valve during LNT regeneration. The method comprises setting a software limit on the throttle valve position. The limit is a dynamic value affected by the engine operating state. A variable relating to the exhaust oxygen concentration is controlled to approach a setpoint by adjusting the intake air throttle valve position subject to the limit. In one embodiment, the valve position limit is based in part on an exhaust oxygen content measured while the throttle valve is fully open. In another embodiment, the valve position limit is adjusted based on the setpoint, whereby greater throttling is allowed when exhaust oxygen content is targeted to a higher value. In a further embodiment, the setpoint is adjusted based on the engine load. The method allows extensive intake air throttling without causing instability in the engine.