Abstract: An engine control system that regulates fuel to an engine after lean idle operation includes a first module that determines a rich mass fuel rate based on a lean operation mass air flow and a stoichiometric air to fuel ratio (AFR) and that calculates a time rich based on the rich mass fuel rate. A second module regulates fuel to the engine during a rich operation period after the lean idle operation to provide the rich mass fuel rate for the time rich.

Abstract: An internal combustion engine adapted for combustion of stoichiometric and non-stoichiometric air/fuel mixtures includes an intake system, a combustion chamber which is adapted for direct injection of a fuel and an exhaust system. The intake port flow output comprises an intake airflow output and an EGR airflow output. An intake port flow estimator determines an intake port gas flow output from the intake mass airflow input of the intake airflow into the intake manifold and the EGR mass airflow input of the EGR airflow of the EGR airflow into the intake manifold using a plurality of engine parameters and an air/fuel adjustment factor. The intake port gas flow output is determined as an effective intake airflow output and an effective EGR airflow output. The effective intake airflow output to the combustion chamber is used to determine an effective mass of intake air output per cylinder.