Idle control on specific conditions

[AVP]

well with the settings i have, my ISV if i take it above 30 it rises the idle and anything above 40 it makes it oscillate like crazy.

[AVP]

mattias,
if you use ignition +/- 5, what value do you use for deg for enabling IAC ?  i presume fairly low so that IAC controls idle most of the times, correct?

[mattias]

With +/- 5 degrees control, I use 4 degrees for enabling IAC to let the ignition advance take care of the small variations.

When you raise to 40% duty cycle and the idle starts to oscillate, figure out why. Check the lambda (VE table problems) and ignition advance. The overrun fuelcut could be the cause, I don't remember at what RPM you set it. The duty cycle that is ok with a cold engine might take it up to the set overrun fuelcut RPM limit. Either way, it was just an interesting experiment, clearly higher duty cycle brings higher RPM which is what you want.

You should also check if the throttle is open a bit, that would explain why you're using lower values than I'm used to with the Audi S4. It could be just right as well.

[AVP]

i have readjusted the throttle plate and that is definitely completely shut.

my overrun fuel resume was on 1500rpm,

now when previously i had disabled PID control and ignition based idle, the idle speed was at 1400rpm and the more duty i gave the higher it went. BUT once i also went below 20PW it also got higher. It stays lower in general when i keep it between 20-30PW.(which is why i have the values i do on those areas.

it is interesting to do this experiment and i will do so and report back.

at least now that i have a working idle so far with my settings, i can try and see what else works.

however other settins such as the ISV hardware settings, also come into play. what do i do with those? do i leave them at 35hz as i have now and min/max as i have them?

[AVP]

i changed the kpa for the fuel cut to 0 and it seems to be much better.

[mattias]

however other settins such as the ISV hardware settings, also come into play. what do i do with those? do i leave them at 35hz as i have now and min/max as i have them?

In a testing phase like this you should set the min/max dutycycle to 0 and 100%, the limits are there to stop the PID to move above/below.

It's obvious your valve is responding only within certain limits and not in a linear fashion, this could be due to using improper PWM frequency. Try to use double the frequency and see if both the useable dutycycle range and max/min rpm changes. It's likely that the proper frequency is in anywhere from 50-100 Hz.

(don't confuse yourself or others by using "PW" - you meant to say dutycycle %)

[AVP]

You would be amazed of how many diff hardware settings I have sen being used successfully on the Audi. Anything fro 25 Hz. To 250.

I use the acronym PW because that is what vems says when you open the table.

[mattias]

I use the acronym PW because that is what vems says when you open the table.

No it doesn't, it says PWM and the column header says "RefDC (%)".

[AVP]

well, it should say what it should mean, why the 2 meanings?

anyway, this is a different topic mattias.

as i said, it appears that managing idle has lots of solutions. I will try and find some time to test your theory of calibrating the idle and once i have some results i will report back.

[mattias]

It says exactly what it means, and it doesn't mean two different things.  PWM = Pulse Width Modulation is done with a specific switching frequency. The duty cycle % refers to the 'on time' vs 'off time'.
http://en.wikipedia.org/wiki/Pulse-width_modulation

Looking forward to some idle testing results from your S2.

[AVP]

i know what duty cycle means but thanks for the info.
when i have more info from the rs2 i will post them up

[AVP]

reporting back from the idle tests...

I did what Mattias suggested, that is ign. idle disabled, integrals all to 0, PID i left it as it is and brought up the idle gauges.

Indeed on cold start the idle DC can be brought up to 40ish to start with and it works fine keeping the idle to the idle speed i want it.

The big suprise though is on warm idle.

On warm idle, any values on the DC below 28 start to bring the idle speed up gradually, from 1050rpm to 1400+ rpm and the lower the DC the higher the rpm goes.

I tried the inverted channel, and it did the same but on the oppposite DC values, ie: idle speed was at it's lowest on 70ish DC and started to go higher for any value above that (80-90 etc)

i eliminated the fuel cut rpm areas and that eliminated the oscillations i was getting as the rpm idle speed climbed, but that had no effect in the ability to manage to lower the idle speed anywhere close to my specified speed of 920rpm.

I tried different values of IAC Hz, with no effect. Anything from 25 to 250 did not change that behaviour.

It is this fact which makes the above behaviour from the IAC integral limit. As mentioned before, once i used IAC dec.limit anything above 10-15 the idle speed started to go up, and that was because the integral was taking the DC into low 20 values and that brought the idle speed up again, as i noticed from manipulating the reference table curve.

So my question to you guys is, why am i not able to get lower idle speed with the IAC alone by giving lower DC values as it should happen?


My setup has the reversed inlet manifold (wagner) and the idle valve is situated in an aera similar to the OEM position. 70mm TPS instead of 60(OEM) and the TPS has been adjusted to be as shut as possible.

when i enable the ignition based idle and the rest of the settings i can get the idle speed a bit lower, but the spark goes into sometimes 5deg when in OEM motronic setup, i usually never goes less than 8 and idle speed is set to 800rpm.

any explanation is welcome.

i do have a log,but it may not make much sense as i had to start and stop the car's engine a lot of times and it may be broken into smaller pieces as a file.

vasilis

[GintsK]

BOSCH two pin IAC has mechanical "limp home" mode. Without current it opens in opposite side allowing to keep idling. Usually about 300rpm over normal when warmed up with no load.

Usual DC on 20VT is around 50% (if you have diode in parallel to IAC). Somewhere at 30% IAC is fully closed. Below 25% it opens again. But on opposite side.

Your situation means: engine get air somewhere else. It should die at 30%. But engine has enough air for idling.

First thing to check is throttle stop screw. Then anything else. Incluiding air leaks.

Gints

[AVP]

i see

i do have a diode working with the IAC.

i have also checked the TPS from the screw and it is completelly closed, so it is not that.

I dont seem to have any leaks, BUT: i do have a dump valve next to the throttle position sensor which on idle it is part open. So air may be drawn through there? that valve is BEFORE the TPS, so as the idle control valve is on that area as well, could it be drawing more air than required and therefore not lowering the idle as it should?

on the other hand, if the idle valve is completelly closed on 30DC, then if there is an air leak somewhere, should it be after the TPS?

here is a photo of the ISV valve at the backround, and the dump valve in front



here is the engine photo

[GintsK]

Dump valve did not feed air to the engine. It simply bypass turbine.

Block IAC hose with plug. Engine should die. If it still works, search for air source.