The purpose of this test is to evaluate the correct operation of the idle speed control valve (ISCV) based on the switching voltage and duty control in response to target idle speeds.
Connection for diagnostic work will vary dependent on application.
Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.
General connection advice
PicoScope offers a range of options within the test kits.
Dependent on difficulty of access, choose from:
Testing sensors and actuators (to include relevant circuit/connectors):
This example of a known good waveform displays a switched-earth, pulse-width modulated (PWM) voltage, actuating an idle speed control valve.
The waveform has a cyclic period in which the voltage switches between battery positive at around 15 V and battery negative at just above 0 V.
The percentage of the total cycle spent at 0 V indicates the PWM duty. This waveform is at 0 V for around half of the cycle, indicating that the PWM duty is around 50%.
One cycle is completed every 10 ms indicating that the cycle frequency is 100 Hz.
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.
The rotary ISCV is an electromechanical device that can have either 2 or 3 connections. One connection will be a constant battery voltage from either the ECM or a control relay, and the others either a 2 or a 3-pin connector, providing a single or double-switched earth.
The single earth system will open the valve in opposition to a closing spring, whereas a double earth system will use one circuit to open and the second to close the valve.
The ECM controls the valve opening position by varying the duty cycle of the switched-earth signal. Therefore, the greater the on time, the further the valve opens allowing more air into the engine resulting in higher idle speed.
Through control of the ISCV the ECM can maintain or adjust the idle speed regardless of changes in engine load caused by the air-conditioning, power steering, automatic transmission, or charging systems, etc.
Due to the location of the ISCV it is susceptible to carbon fouling. As such the valve may be electrically functioning with a normal waveform but is mechanically faulty. The symptoms remain. In this situation the valve must be removed for examination, cleaning or replacement.
P0505 Idle Control System Malfunction
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected
P0508 Idle Air Control System Circuit Low
P0509 Idle Air Control System Circuit High
P050A Cold Start Idle Air Control System Performance
P0511 Idle Air Control Circuit
P0518 Idle Air Control Circuit Intermittent
P0519 Idle Air Control System Performance
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.