The purpose of this test is to evaluate the Idle Speed Control Valve (ISCV) control signal from the Engine Control Module (ECM).
This known good waveform has the following characteristics:
An ISCV is used by the Engine Control Module (ECM) to regulate engine idle speed according to engine temperature and load when there is no driver demand from the accelerator pedal and the throttle is closed.
For example, during cold start conditions, the ECM will seek to quickly raise engine temperature by increasing engine speed to a fast idle, at around 1200 rpm.
With an ISCV, the ECM can maintain and adjust the idle speed for changes in engine load caused by the air conditioning, power steering, automatic transmission, or charging systems, etc.
The ECM controls the valve opening position by varying the switched earth signal; the greater the average voltage, the greater the average solenoid current and the greater the valve opening.
Due to its location, the ISCV is susceptible to carbon fouling. As such the valve may be electrically functioning with a normal waveform but mechanically faulty. In this situation, the valve must be removed for examination, cleaning or replacement.
Symptoms of a faulty ISCV:
Causes of ISCV failure:
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