IAC PWM freq?

[ranz]

I have installed couple of PnP VEMS units to different cars (S4, 200, S2) and all of them have the IAC PWM freg 250Hz and they work wery vell. Now on my S2 I use standard vems ecu (my own harness) and I had to put the freq as low as 20Hz to get the car to idle fine. I tried another IAC also, same thing... why do I have so low freq?
It´s not a big problem, because car runs wery well and everything is fine... but so low freq makes this funny clicking sound

[rob@vems.co.uk]

Have you got a flyback diode across the IAC solenoid?

[ranz]

Have you got a flyback diode across the IAC solenoid?

No, all the cars run without the diode. On one car I tested if the diode makes any difference, it did not, so I have not used it on any car. But that was on my mind also, maybe that helps to get the freq higher?
But if it does, how the other cars work witout it?

[rob@vems.co.uk]

I thought the flyback was inside the PnP, but its possible it isnt.
Try one anyway.

[ranz]

I thought the flyback was inside the PnP, but its possible it isnt.
Try one anyway.

Maybe the PnP has the diode inside and the standard ecu has not... thatswhy other cars work and mine does not, i´ll try it.

[AVP]

hi ranz,
im also interested in the IAC PWM. what kind of sound does the valve do? Im currently on 1.1.27 and the megatune attribute of PWM frequency, i had it set to 0 and then max steps to extend 110 to get it to work right. Its not ideal but at least it reacts ok.

I do have the diode, as an extra cable between the harness and the IAC.

would it be possible to send me a photo of the IAC settings you have at the moment, as well as the others you have used succesfully on the audi engines?

I have found that the position of the IAC plays a role in the responce for some reason. I had to slightly alter the PWM frequency against temp when i used a reverse inlet manifold and changed the position of the IAC.

thanks
vasilis

[ranz]

I don´t know how to say what sound it makes... it´s just fast clicking, other cars have the freq so high that you dont hear that click.
Here is idle setup from one audi 200 with AAN engine, 1,8T coils, original cams, revers intake and 900CC injectors.





Ignition advance and spark-cut idle are disabled

[AVP]

thanks for that ranz

do you use the same settings but with 20hz PWM on your s2?

[ranz]

thanks for that ranz

do you use the same settings but with 20hz PWM on your s2?

Almoust yes, there are some wery little differences on some numbers (TPS value for idle thereshold is 3, idle RPM warm engine is 850, etc), only the valve reference position tabel is a lot different, and the freq is 20Hz.
And one other car (audi S4, original AAN engine with RS2 injectors) has everything same as the 200, but slightly different reference position table.

[AVP]

it is very interesting to see these settings. In 1.1.27 i had to start the PWM frequency from 0 (as if working only on ignition timing based idle when cold) and gradually put the IAC into the game and have it control the idle when warm. I see now that the PWM reference position table is going from higher values to lower.

I guess i have to see in action what would work for me,but thanks for the valuable info!

[ranz]

it is very interesting to see these settings. In 1.1.27 i had to start the PWM frequency from 0 (as if working only on ignition timing based idle when cold) and gradually put the IAC into the game and have it control the idle when warm. I see now that the PWM reference position table is going from higher values to lower.

I guess i have to see in action what would work for me,but thanks for the valuable info!

BTW, these car have FW 1.1.74 and my own has 1.1.81.

[Jamo]

Very strange my car idles perfectly on 1.1.74 and 1.1.81 with the IAC on 75 hz

[mattias]

After doing a bunch of PnP installs on S2/S4/S6 cars I find that only one out of ten have a fully working ICV..

Start with integral  limits at 0, then adjust the reference table and try to see if the valve reacts to your inputs in that table.  Try to change frequency settings if you wish, 75 Hz is a perfectly fine setting and should be unless the ICV is broken.

Don't enable the integral limits until you feel that the valve is ready to regulate the idle, when you do the PID parameters take over and can really make your life miserable if not set properly. Do NOT mistake poor PID tuning for a badly functioning valve. Make sure it reacts to your fixed duty cycle changes first (ref dc table).

It helps if you (in VemsTune) set up  gauges for: idle target rpm, idle duty cycle and idle int.

[AVP]

thanks for that mattias. its a good start. I always use small integrals, and on 1.1.27 had a good reaction, but once upgraded ill follow this advice!

[ranz]

My problem got solved after installing the diode:D now the freq is 250Hz and the clicking sound gone