[Eiska]

Hi
So i have a weird issue with my 3 wire iacv.
Its a bosch 3 wire style 0 280 140 575.
It is slightly open all the time (tps at 0% but idling at 2k rpm)
I can raise the idle with the duty cycle but i cant lower it, it doesnt lower the rpm at all

What should i do?

Thank you

[Eiska]

Oh and i nos remembered.
Middle pin obviesly has 12v switched.
I noticed if i remove one of the side pins it increases rpm like crazy and if i remove the other pin it does nothing.

[PSIG]

The 3-wire IACs are powered on one wire, and a push-pull PWM on the other two wires. So 100% PWM on one wire and 0% on the other will fully rotate the valve one way or the other. 50%/50% will hold at a mid-way point.

Also, I have not used that specific valve, but most of them are slightly open when fully closed as a "limp home" high-idle function. Increasing opening actually closes the valve more for reduced idle. Opening farther with then increase rpm above low-idle.

I hope this info helps you to find what your valve is doing. This graph represents the operation:

[pazi88]

If the idle is too high, even when the valve is fully closed and you can only increase RPM. It means that you either have vacuum leak or the throttle flap itself is open so that it idles high. Usually you shouldn't have any air leakage from the closed throttle flap or anywhere else in the system. And all the air that engine gets when idling, is from the idle valve.

[Eiska]

I did some more testing today.
I noticed the valve is either fully closed, fully open or half way open when i change the wires around.
I tested to adjust the duty cycle 100% 50% and 0% and it does nothing even when the wires are changed around.

[dazq]

I did some more testing today.
I noticed the valve is either fully closed, fully open or half way open when i change the wires around.
I tested to adjust the duty cycle 100% 50% and 0% and it does nothing even when the wires are changed around.

Sometimes changing the frequency of the pwm improves the resolution that the change in pwm duty has on the movement of the actual valve.
You may also find that a back emf diode on the valve coil (coils in the case of a three wire valve) also has a substantial effect on the operation. It also usually makes the driver fet run a lot cooler too.

[Eiska]

I did some more testing today.
I noticed the valve is either fully closed, fully open or half way open when i change the wires around.
I tested to adjust the duty cycle 100% 50% and 0% and it does nothing even when the wires are changed around.

Sometimes changing the frequency of the pwm improves the resolution that the change in pwm duty has on the movement of the actual valve.
You may also find that a back emf diode on the valve coil (coils in the case of a three wire valve) also has a substantial effect on the operation. It also usually makes the driver fet run a lot cooler too.

I tried to change frequency ranging from 10hz to 120hz and also changing duty cycle wich does nothing on it.
All it does is it goes back and forth either slow or fast. At certain frequnecyes it is almost closed.
Changing pwm cycle on differend frequencyes does nothing.
Only one that works ”right” is the on/off that opens the valve half way at a certain temperature.

I am sorry if i dont andurstand every thing this is my first time doing standalone ecu stuff. Also sorry for bad england.

[PSIG]

Just to be sure for wiring, I would test ohms on all IAC pins. Incorrect wiring could cause the symptoms you have. With one probe on the 12V power pin, the ohms on each other pin should be similar. If wired wrong, the other 2 pins will have very different ohms.

Poor example of operation - the IAC valve is spring-loaded and resists movement. Operation works like 2 motors against each other. Motor1 tries to open the valve against the spring, and motor2 tries to close the valve. When powered equally (or off), the valve is still. When motor1 is powered more (or motor2 powered less), the valve turns that way against the spring. A little more, it opens a little against the spring. A lot more, it opens a lot.

If it helps concepts - old control methods were only 2-wire (power and one PWM), with the 3rd wire connected through a power resistor to ground. Typically 50-ohm, 50-watt. This is like the example above, but with a constant force on motor2, and PWM to motor1 varied pressure against motor2, the valve and spring.

Frequency (Hz) affects control range. Lower frequency (50-150 Hz) gives good authority across a wider range of PWM, but is noisy. Higher Hz is quieter, but narrows the control range (less control). It is a compromise. Hope that helps.

[Eiska]

Just to be sure for wiring, I would test ohms on all IAC pins. Incorrect wiring could cause the symptoms you have. With one probe on the 12V power pin, the ohms on each other pin should be similar. If wired wrong, the other 2 pins will have very different ohms.

Poor example of operation - the IAC valve is spring-loaded and resists movement. Operation works like 2 motors against each other. Motor1 tries to open the valve against the spring, and motor2 tries to close the valve. When powered equally (or off), the valve is still. When motor1 is powered more (or motor2 powered less), the valve turns that way against the spring. A little more, it opens a little against the spring. A lot more, it opens a lot.

If it helps concepts - old control methods were only 2-wire (power and one PWM), with the 3rd wire connected through a power resistor to ground. Typically 50-ohm, 50-watt. This is like the example above, but with a constant force on motor2, and PWM to motor1 varied pressure against motor2, the valve and spring.

Frequency (Hz) affects control range. Lower frequency (50-150 Hz) gives good authority across a wider range of PWM, but is noisy. Higher Hz is quieter, but narrows the control range (less control). It is a compromise. Hope that helps.

Hi
I measered from the center 12v pin to sides and i got 14.5 and 16 ohms. And across it was 31 ohm. The iacv is brand new it should be fine.
Could that 50ohm 50w resistor work on a 3 wire iacv?

[PSIG]

I have not tried it with you specific IAC version, but it has worked with other Bosch valves in the past. <shrug> For that, it would be 12V on one pin, and only the primary IAC PWM wire, with the 3rd wire to the grounded big resistor. This was popular with the old MS-1 and similar ECMs designed for 2-wire IAC operation. Best of luck if you try it.