Engine rotation speed control system

An engine rotation speed control system for automotive vehicles having an internal combustion engine comprising a carburetor having an air intake passage, an intake manifold and a throttle valve disposed intermediate said air intake passage and said intake manifold, air passage means by-passing said throttle valve disposed in communication with said air intake passage and said intake manifold, a solenoid actuated valve provided with a solenoid coil disposed in said air passage means for controlling the amount of air by-passing said throttle valve when said throttle valve is closed during idling, a battery for supplying electric current to said solenoid coil, a resistor connecting said battery and one end of said solenoid coil, first and second switch means connected in series with each other and connected in parallel with said resistor, ignition switch means controlling said first switch and temperature sensitive means controlling said second switch whereby when said ambient temperature surrounding said engine is below a predetermined temperature said first and second switches will be closed upon operation of said ignition switch to by-pass said resistor and increase the current supplied to said solenoid coil.