Abstract: A control system for adjusting the amount of a secondary air to be fed into the exhaust system, comprising a secondary air control valve (ACV) for controlling the amount of the secondary air from an air pump, vacuum switching valves (VSV) alternately effecting an operative vacuum on the ACV, and a vacuum control valve (VCV) which is connected to the VSV via a first vacuum reservoir tank and to the intake vacuum area via a second vacuum reservoir tank.

Abstract: A system for introducing secondary air into gas exhausted from an internal combustion engine of the carburetor type, provided with a three-way catalytic converter in the exhaust system of the engine. The system includes a flow control valve having a diaphragm operated valve member for controlling the amount of secondary air in accordance with electric signals from a .lambda.-sensor arranged in an exhaust system of the engine so that excess air ratio .lambda. of the exhaust gas, which is introduced into the three-way catalytic converter, is controlled near 1.0. Therefore, effective cleaning operation of the three-way catalytic converter is expected.