Idle Speed Control Valve

The type of idle speed control device we used was a rotary type and base idle is adjusted using the ECU, and the cold/fast idle speed is activated by the engine temperature, which uses a bi-metallic strip wound up. When it is cold (by engine coolant), the strip opens the valve up. As the engine warms up, the two metals expand at different rates, causing the strip to wind up more and close off the valve. At this point, the ECU takes over to control the base idle.
To test the device, we use a multimeter, setting it to Duty cycle or frequency and test the RSO (open) and RSC (closed) with the negative probe on the earth point. We can also check the resistance between the RSO and RSC windings. The resistance between the RSO and RSC windings were 20.1 and 19.9 ohms. The duty cylce percentage is how often the valve is open or closed. Testing the RSO we got 63.3%, which means the valve is open 63.3% of the time when the engine is at idle. We then tested RSC, and by maths we should have got 36.7%, and we got 38.7% which means the IAC is closed 38.7% of the time.
We also tested the frequency of the IAC. The frequency is how often the valve opens or shuts per second, and is measured in Hertz (hz). For the RSO, we got 244HZ which means the IAC opens 244 times per second. Also, for RSC, we got a reading of 244 HZ, which means the IAC closes 244 times per second. Because there is no variance in frequency between RSO and RSC, it means that the idle speed is being adjusted by the duty cycle percent.