Various sensors including throttle position sensors (TPS), manifold pressure sensors (MPS), crank angle sensors, engine temperature sensors, and oxygen sensors are mounted in electronically controlled fuel injection (FI) systems to accurately regulate the air-fuel ratio according to the operating state and operating environment. Among these vehicle-mounted sensors, TPS has functions for detecting a fully-closed throttle and estimating intake air volume by the amount of throttle opening. Currently, we have conducted a study on transferring TPS functions into the MPS (manifold pressure sensor) in order to eliminate the TPS. Here we report on detecting a fully-closed throttle for achieving fuel cut control (FCC) and idle speed control (ISC) in fuel injection systems.We contrived a means for fully-closed throttle detection during ISC and controlling changes in the bypass opening during FCC in order to accurately judge each fully-closed throttle state via the manifold pressure. A factor in causing fluctuations in manifold pressure in a fully-closed throttle state are changes in the engine RPM (also referred to as engine speed) and changes in the degree of opening of the bypass (hereafter simply bypass opening). By keeping the bypass opening during FCC we limited the cause of fluctuations in manifold pressure to just the engine RPM; and by comparing the manifold pressure with an manifold pressure threshold equivalent to a fully-closed throttle detected at each engine RPM, we were able to accurately detect fully-closed throttle states. Another achievement was detecting a fully-closed throttle state during idling for performing ISC. This ISC adjusts the bypass opening in order to converge the engine RPM during idling to the target RPM. In other words, the manifold pressure during idling fluctuates due to two causes or namely the engine RPM and the bypass opening. So by comparing the manifold pressure with a manifold pressure threshold value equivalent to a fully-closed throttle state from the bypass opening and engine RPM we succeeded in contriving a method to detect a fully-closed throttle state with good accuracy. We found that this control technology accurately achieves fully-closed throttle detection by manifold pressure which is one of the TPS functions.