| 摘要 |
PURPOSE: To improve diagnosis precision and to simplify discrimination of whether defective operation of an ISC valve occurs on the opening side or on the closing side. CONSTITUTION: It is discriminated whether the number Ne of revolutions of an engine during idle operation is within the allowable area±ΔN of the target Ne0 of revolutions. An absolute value|Ne0-Ne|of a difference between the two numbers of revolutions is compared with the preset allowable number N of revolutions at S3. When the number of revolutions of an engine is outside an allowable region, in a case of NeO>=Ne, diagnosis on the low rotation side is executed, and in a case of Ne0<Ne, diagnosis on the high rotation side is executed. In diagnosis on the low rotation side, a duty ratio Duty of a drive signal for an ISC valve is compared with an allowable maximum value DMAX at S5. In diagnosis on the high rotation side, a duty ratio Duty is compared with an allowable minimum value DMIN at S12. When the duty ratio Duty exceeds an allowable maximum value DMAX or is reduced to a value lower than an allowable minimum value DMIN and besides this state is continued for a set time, it is decided that a trouble occurs in such a manner that in diagnosis on the low rotation side, the ISC valve is not operated to the opening side and in diagnosis on the high rotation side, the ISC valve is not operated to the closing side.
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