Catalytic converters in automobiles now number in the millions. All of these devices are periodically forced about the stoichiometric air-fuel ratio at a frequency of about 1 Hz and a small amplitude. Experiments show that this periodic forcing suppresses rather than enhances conversions under normal operating conditions, even though many publications demonstrate that large rate and conversion improvements do occur for the converter reactions over the individual noble metals used in the three-way catalysts. This review concludes that improvements are not found because enhancement becomes very small in the 400-600 degrees C temperature range and forcing at about 1 Hz is sub-optimal.