Spark ignition type engine

A spark ignition type engine comprising:

• a main intake-air passage;
• a throttle valve of the main intake-air passage;
• a bypass intake-air passage bypassing the throttle valve;
• an ISC valve of the bypass intake-air passage;
• and an electronic control device that controls an engine speed by adjusting an opening degree of the ISC valve,
• wherein when the engine is started, cranking is performed at a cranking opening degree at which the ISC valve is narrowed by a predetermined amount from a fully opened state by control of the electronic control device, so that an intake-air negative pressure is generated on an intake-air downstream side of the ISC valve,
• the engine comprising:
• an engine temperature sensor;
• and an atmospheric pressure sensor,
• wherein
• as a detected engine temperature becomes lower, a base lower limit value of an ISC valve opening degree is increased to a fully open side, and
• the base lower limit value is corrected to increase to the fully open side with an increase correction value based on a detected atmospheric pressure in an engine middle-high temperature range where the engine temperature exceeds a predetermined value, and in the increase correction, the increase correction value is increased to the fully open side as the detected atmospheric pressure becomes lower, and
• the increase correction is prohibited in an engine low temperature range where the engine temperature is equal to or lower than the predetermined value.