Engine air/fuel ratio control system with both normal idling and idle up idling capability

For an internal combustion engine comprising an exhaust system and a fuel intake passage system comprising a carburetor which comprises an intake throat, a throttle valve mounted in said intake throat, and an idle up device which selectively acts on said throttle valve so as to control its most closed position to be either a first idling position near its fully closed position or a second idle up idling position slightly more open that said first idling position;

• said carburetor in its basic operational mode tending to deliver an air/fuel mixture richer than stoichiometric:
• an air/fuel ratio control system, comprising:
• (a) an oxygen sensor for detecting the concentration of oxygen in the exhaust gases in said exhaust system;
• (b) a means for adjusting the air/fuel ratio of the air/fuel mixture being supplied to the engine through said fuel intake passage system towards the leaner, which receives the signal from said oxygen sensor, and which functions only when said sensor is detecting no oxygen in the exhaust gases in said exhaust system;
• (c) a means for supplying a flow of secondary air into said exhaust system during idling engine operation, upstream of said oxygen sensor, in a flow amount sufficient to render the exhaust gases in said exhaust system leaner than stoichiometric, said means thus supplying secondary air when and only when it receives supply of a controlling vacuum;
• (d) a first vacuum takeout port formed at a point in said intake throat which is downstream of said throttle valve when said throttle valve is in said first idling position but which is upstream of said throttle valve when said throttle valve is opened a slight amount from said first idling position;
• (e) a second vacuum takeout port formed at a point in said intake throat which is downstream of said throttle valve when said throttle valve is in said second idle up idling position but which is upstream of said throttle valve when said throttle valve is opened a slight amount from said second idle up idling position;
• and
• (f) a vacuum switching system, which provides supply of vacuum from said first vacuum take out port to said means for supplying secondary air as said controlling vacuum when said idle up device is controlling the most closed position of said throttle valve to be said first idling position, and which provides supply of vacuum from said second vacuum take out port to said means for supplying secondary air as said controlling vacuum when said idle up device is controlling the most closed position of said throttle valve to be said second idle up idling position.