VEMS: the unstoppable pulsing idle

[QuattroFever]

Show us your configfile please....

I don't use PID idle, only ign. based and it is very stabile with it !

Thomas

ok...

wont let me upload my config file or log. says "invalid file"

[A80Avant]

for the idle issue i had a nice guidethrough by mattias which helped me.

1) turn OFF ignition based timing
2) turn OFF PID (use PID 0/0/0) and put integral limts to 0 as well
3) get the DC% curve fixed, so that when you have the engine cold, you manipulate the DC in a way that your cold idle is always reached. Do this until the PW is made up till the engine is warm.

Then you can turn on the ignition based idle and that will help with the keeping of cold and warm idle.

You can now set the integral limits as high or low required to allow for the PID to make any correction.

Now for the PID, you need to find a solution that once the idle is NOT where it supposed to be, that it actually requires the minimum of values to get it to the right rpm speed.
I usually do that by doing standing presses of the accel pedal and see how much time it takes for the idle to set back to the warm idle speed without oscillations. Start by giving values to the P and then adding the rest in.

Using large numbers on PID, such as more than 50, means that the PID sequence will do large steps to try and correct the idle speed when off balance and that may take a lot of time to rest (oscillate). Therefore you need rather small values esp. if the DC curve of the IAC is set correctly.

I use now something like 18/6/2 and it does the job, no oscillations and very minimal dip when ALL electrical connections are operational, which is a good thing.

Finally, an easy way to tune P is to keep putting large values, until you see that if you press the accel and release it, the needle is actually not able to settle on idle speed, but keeps oscillating continuesly. Then you need to use half that P value and maybe a bit less than that.

Also, on our IACs, any DC less than 29-30% keeps the IAC completelly closed. That means that if you dont have any air leaks, and the TB is completely shut, the engine should stall or the idle should drop quite a bit. Therefore if that is not happening, look for leaks or calibrate the TB. Generally you may find that the DC of the IAC should be something like from 50 on cold till 35ish on warm engine depending on setup.

On my car, i noticed that using larger values on the D, made the needle to drop after an offset from the idle speed. So i reduced it.

as for ignition timing idle, i use about 10-15deg +/- and change of 25deg every 256 eng.cycles.

i use 30Hz as hardware and i use min of 29%DC as anything below that reopens the IAC and gets the idle speed higher! Be aware!

[QuattroFever]

hmm, interesting. I ended up at that figure 29 min dc too. Any lower and it constantly stalls when dipping the clutch so that makes perfect sense. At 29 i get revs drop to about 300rpm on pressing the clutch but it recovers. I managed to smooth it out a little by turning ego correction off till 2000rpm. If i could post my log you can see that the afr is up and down at idle between 15.5 and 14 and at its worst when the fan cuts in. If i set min dc to 32 it stops the revs dip problem but it idles at like 1200-1300. Maybe an air leak then, ive been round and tightened everything and on a pressure test the PCV valve was leaking from a small square hole in its top not sure if its supposed to do that?

[A80Avant]

the dip in the revs when the clutch is pressed could be an entirely different problem. What are your settings on fuel cut and fuel resume regarding overrun fuel cut?

also, what kpa have you used to have a fuel cut on? Its in the same settings area as the above, under safety/overrun

put the fuel cut and resume at 1600/1500rpm respectivelly and put 0kpa for fuel cut as well. Then see if you get the clutch/dip revs issue.

Since you have the OEM TB, it is likely that the DC on around 29 or a bit lower is actually working much better to show where the IAC is completely shut. You dont neceserraly have a leak under these conditions, its just that the oscillations that are caused as the DC goes lower than 29 represent the opening and closing of the IAC.

[Jamo]

Considering all I5 cars are mapped from the factory to run richer below idle, I'd say something is wrong.
If I map my car too lean near idle, then there is hesitation - like something is holding the car back, when you are starting.

Could you clarify this are you saying that cars are set to run rich at idle or that if they go into vacuum they go richer?

[Billman]

Actually he said below idle.

[prj]

Yes, below idle.
If engine starts stalling it enriches mixture... for OP it was the other way around, so I suspected a problem.

[Jamo]

Thanks I feel a change to my lambda table coming on