VEMS : revs rpm dropping off when engine loaded

[ranz]

Now try to rev the engine and close the trottle to see if it catches it. The pid`s D, is 150 and i see that on most cars if the D is to low, the car got stalling issuses.

I had the same issue with previous FW 1.1.85, but now with 1.1.88 it seems that it also works with low D (previous FW also had boost PID issues), I played with it yesterday a little and finished with D only 9 and it catches idle wery good.

[A80Avant]

may i say that reidar has a nice explanation there BUT i have to say this to people who think that previous firmwares have had problems with idle. I dont believe it.

i am still on 1.1.81 and my idle is responding to changes nicely. I use much smaller values on the PID (something like 20/12/2) and much larger on integral limits and that allows the PID to make big changes if needed but slower!!!!

If you use large PID values, then the ECU is trying to correct a problem making large steps. However, if your integrals are tiny (such as reidars) then the amount of intervention from the PID you allow is very small, so its like shutting it off!. If your idle is always close to the desired/specified value of say 900rpm then all settings (ignition timing, IAC control, etc) do not have to do a lot of work to get it right.

In my opinion the PID is there to prevent over and under shoots, and if the rest of the settings are set properly, then it will react nicely to problems like high load and such.

Quattrofever: PID values will have NO effect whatsoever on idle unless you blib the throttle while channging them in order to see what happens to the idle as it tries to set back down to your desired value. PID is trying to control idle when it is away from it. So the easiest way to test your PID is while you make a change in the values, you blib the throttle slightly all the time and allow it to rest to the idle value and see what happens. Does it overshoot? does it undershoot? does it die? etc. Ideally you do that with all electrics on, find a PID setting that works there and then turn all off and see how much different that is (ie how higher the idle sets with all electrical equip off.)

In my opinion, as Raydar writes, the beginning of the procedure is right, BUT once i put in the ignition based timing settings, i DO NOT recalibrate the ref. curve. I leave it as it is, because that means that if i do that, then i dont know how the ignitiion based timing will eventually react to changes, and what the final outcome will be.

If i fix the curve and i have a value of say 35 to keep an idle of 900rpm @ 75C of coolant temp, and 15deg of advance, and once i turn the ign. based timing ON, then the idle drops or changes from that position, then there is something else wrong. Either some of the ign.timing settings are fishy, or the curve is not correct, because if my desired idle is reached by the curve alone, then ign.timing SHOULD NOT affect the idle even when turned on. Ign. timing and PID are there to control offsets of idle NOT the idle itself. That is done by the ref curve of the ISV.

Quattro, i think the best way to help you is to try and meet up at some point so i can see in person what the idle is doing.

I have to say, i use EGO on, my VE table is set to be almost 100% (ie zero) on idle for correcting to desired lamda, and even though i have a slight problem with my throttle valve being 70mm and allowing some air to pass through,therefore giving me higher idle than what i could get, i now have a specified idle speed of 950rpm, ign.timing of motronic value(my motronic had about 8-10deg advance on warm idle) and the engine feels like stock. No overshoots except one position on warm up at about 45-50C which for other reasons it tends to drop a bit as i go to neutral. But that corrects itself at 55C . it must be related with my warmup enrichments.

[ranz]

may i say that reidar has a nice explanation there BUT i have to say this to people who think that previous firmwares have had problems with idle. I dont believe it.

i am still on 1.1.81 and my idle is responding to changes nicely. I use much smaller values on the PID (something like 20/12/2) and much larger on integral limits and that allows the PID to make big changes if needed but slower!!!!

You may or may not belive it, but we discussed it on another topic where I played with my idle settings and I DID NOT get stedy idle unless I raised D over 150. I tryed many tutorials how to set idle correctly etc. etc. etc. ended up pretty much on same spot.
Now last week I chaged FW, the settings stayed the same (D: 170) and it worked well, but yesterday I connected shift light, launch and shift cut and because of that topic I also tried what idle does when I turn on air vent, lights and rear widow heater, the idle was not dropping below 800 (it's set to 850)... also I tried lower the D to 2, to 5, to 10 and ended with 9 because now it works with that also with previous FW with that low D the RPM dropped down to 600 and then catched the preffered 850 when revs come down.
So, the FW is important here! also, cars with similar setup (lets say original setup) also need different settings, two similar cars do not work well with same settings.

[A80Avant]

You cannot say that PID settings are right or wrong unless you see the idle as a whole. I know that we have discussed this before but then I had a talk with Matthias and another bend developer who explained to me the things I am suggesting above. It may be that by using previously so high D value you could have reached a level of inactivity it noise of the PID system that it made it work. Who knows. I tried your 150 setting once and didn't work. Ad I said, now I'm still on 1.1.81 and my D value is 2.

[ranz]

I tried your 150 setting once and didn't work. Ad I said, now I'm still on 1.1.81 and my D value is 2.

Just for information, what your cars idle made with 150 D? did not idle correctly, did not catch idle, or when the vent/heater where turned on and it dropped? or something else?

[Reidar]

A80Avant:
I dont say that older FW`s got issues with idle, i just say that you cant expect my configs to work with different versions. Cause there ARE differences on some FW versions.
These PID settings are quite extreme yes, and dont look much like my usual settings, but it should defenetly do something to his idle. I even got this working quite good with a car running AC, and aprox 60rpm drop in idle when ac on.

I use the ignition adv. as a measurement to see how much my refDC is off, cause it`s sometimes hard to just set it right te first time and have the car idle perfect. I switch on and off the ignition adv. to see for changes. In my opinion, if the ing.adv is off after you have changed your refDC, it`s trying to compansate for something, and usually that is the redDC. atleast if the other settings are correct

I have noticed that heatsoaking the MAT allso gives issues at idle and temp changes. EGO ON, usually fix these problems, but some car`s dont use a WBO2 even tho I recomend it. then changes to the mat/tps fuel table is needed at 0% trottle.

ranz: I belive you And yes! two different car`s often need totaly different settings. I dont think I got one config with the same idle settings, and i probably got atleast 50 configs from different cars, or cars witch have been modified since my first config.

[A80Avant]

I agree with you Reidar! It's funny how so many cars with similar equipment can have so different settings and yet work!. I think there are variables that each one of us take for granted but have an effect in idle, which is why there are differences.

On D 150 ranz, my idle was fine once I switched the engine on, but once I slipped the throttle, the idle never came back to 950rpm, but stayed at 1200. I have read about PID tuning and that was to be expected. So for that value to work for you, you must have had some other different settings to mine.

[A80Avant]

By the way, you will always see some drop on the revs under load,hell that happens with motronic as well. The idea is for it not to stall. Mine now drops to 900ish under full electric load, and it never plummits.

[prj]

By the way, you will always see some drop on the revs under load,hell that happens with motronic as well.

Yup, it does.
Motronic regulates idle using ignition and the ISV. Smaller changes are "caught" using ignition until the ISV catches up. On larger changes, such as the AC, it'll dip a bit, because an ignition adjustment won't be enough and ISV reaction is not instant.

[QuattroFever]

this is different. You mean when the fan cuts in and the idle speed drops. Mine is dropping off on the overrun.
It idles ok but when you rev it and go to pull away its dropping below to about 500rpm and stumbling three times then pops back up to idle speed with hardly any oscillation once it recovers.

Afr goes lean -> 18.9 as it comes down from rpm. Whether you blip the throttle, coasting to a stop, suddenly press the clutch etc.

Fuelcut shouldnt be active but its the kind of symptom youd expect if it was.

[QuattroFever]

a log would help. Will get one up.

[ranz]

dropping off on the overrun.
It idles ok but when you rev it and go to pull away its dropping below to about 500rpm and stumbling three times then pops back up to idle speed with hardly any oscillation once it recovers.

I had same problem and only thing that helped was to rais D to over 150, on my own car I used 170.

[QuattroFever]

aaaaaaaaaaargh! This is driving me insane!
You think you've got it nailed and then it does something random.

Been at it since 7.30 blipping the throttle in tesco. Even the trip computer was flashing 2:00 at me an hour ago telling me to quit.

P - 10
I - 20
D - 170

Integ. Decr. - 5
Integ. Incr. - 35

Was great! Shut it off, checked oil ready for a run, started back up and its bouncing up to 1400 then down to 900
Wtf is with this?

[Reidar]

pleas share a config or logfile, so we can have a look at it

[A80Avant]

mine was doing something similar when the D was that high.