| 摘要 |
To provide a water temperature sensor failure detecting device for an idle speed control system of an internal combustion engine which eliminates the need for a bimetallic guard mechanism, an aperture characteristic of an idle control valve (ISCV) when normal becomes a larger degree of opening as coolant water temperature drops, and bypass airflow supplied to an engine is increased. During failure of a water temperature sensor, a duty value for driving the ISCV is set at 50%, the ISCV is opened substantially halfway, and the bypass airflow supplied to the engine is caused to be a neutral flow. In this way, by causing the bypass airflow during failure of the water temperature sensor to be a neutral flow, a worst state of overrun, engine stall and the like can be prevented, and startability when at low temperature and operability after engine warmup can be ensured.
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