Engine does not go back to IDLE correctly

[ranz]

Car idles well, no problem with that, but when I rev up and release the throttle, it does not go back to idle correclty, it droppes down to 600RPM, then again up, down and then stayes to around 900RPM, sometimes the engine stops because of that.
I tried different settings to get rid of it, but nothing seems to be helping... does anyone have any ideas what to change?
Log: http://ranz.planet.ee/idle.vemslog 56 seconds to 1.02

[gunni]

Look at what the mixture does,
does it go lean or rich, is there any pulsewidth at all ?

[ranz]

Look at what the mixture does,
does it go lean or rich, is there any pulsewidth at all ?

Yes it seems that fuel comes back from overrun a little to late, overrun settings are 18kPa, fuelcut @ 2700RPM and resume @ 1800RPM, but somehow it resumes fuel @ 900RPM and that seems to be too late. I do not recall right now, did it do the same thing if the overrun was deactivated... I´ll try it today.

[ranz]

Seems that without overrun fuel cut it´s even worse

http://ranz.planet.ee/idle2.vemslog

At first there is no overrun fuelcut, RPM drops down to 500, second and third are with overrun fuelcut.
But it´s not right... something is still wrong, why it drops below 900RPM?

[mattias]

There are a number of things you can try  :

Your ignition timing table is quite relevant to what the IAC algorithms can do.  If 900 rpm is your target for  hot idle, then add a column at 900 (right click 700 column heading, "insert") and set the advance there to what you really want at idle. From your log it seems it's at 13 degrees while keeping a steady 900 rpm idle.  Set all cells in the 900 and 1200 column, 46 and 30 kPa row, to  15 degrees. Also set 20 degrees at 700 at 66 and below. This gives a natural advance that should work with just a throttle stop and no idle air valve with PID control.

Enable ignition advance control as a last measure, give it +/- 5 degrees control, IAC threshold to  4 degrees - it calls on extra air if more advance change than that is needed to maintain target idle rpm. I usually set the rate to 25 degrees/250 rpm to get a lightning fast adjustment.

I'm not sure 250 Hz is the correct frequency for this valve, try lower like 50-75 Hz.

Under PWM Idle control dialog, set reasonable max/min allowed duty values, if you idle well at 40% then set the min value to just below like 39%. If a hot summer day with hot MAT readings requires more, cure that with tuning the "refpos addition for MAT, slope".

You should look over your IAC duty % while cranking, 10% cold and 100% hot is not always the best situation. Try using your hot idle duty % for both hot and cold to start with.

I usually use a couple of % higher duty in the ref table, and use more "integral decrease" (and basically no "increase"). That way the valve closes to keep rpm down, rather than the opposite.

Don't do it all at once, try to be systematic when going about this. I would start with a decent ignition table. We could really use a separate ignition advance table, hopefully in a not so distant firmware revision.

BTW, your MAT/TPS fuel enrichment table is all shot to hell, replace it by drag'n'dropping one of the default firmware configs on the table for that dialog. You currently have very poor compensation for the basic natural laws, cold air = more fuel, hot air = less fuel.

[GintsK]

It is still question - what circumstance cause so low overrun rpms. It looks like main reason here.

[mattias]

I never use both the pressure based and the RPM based overrun fuelcut at the same time. I prefer the RPM based one every time.
In this case, if you have to keep it,  maybe use 15 kPa or less, to make fuel resume at a higher RPM.

[Sprocket]

The bottom lines below the idle kpa on the fuel map are just as important as all the others. On over run the MAP will reach the bottom of the map. If RPM is above fuel cut resume, the engine is pumping air. If the VE values are rich and the EGOC settings enabled in this area of the map. Once the RPM falls bellow fuel cut resume value, the rich VE value over fuels the engine and EGOC starts to remove the fuel. RPM quickly approaches idle which is usually quicker than it is for EGOC to put the fuel back in. Result - lean condition low RPM = stall

Things to look out for in the log after an over run event. Rich condition straight after fuel resume, EGOC removing fuel, then a Lean condition around idle set point.

I am not sure how the newer firmwares deal with this as I have not had a chance to try them yet lol, but it was something I became aware of from 1.0.73 right up to 1.1.47.

If you can, tune the lower VE lines so that around fuel resume they are ever so slightly lean, this way EGOC adds a little fuel.

Oh and I just looked at the insert feature on the tables, and I have to say, I am well impressed with it it even extrapolates the new values. I never knew it was there 

[GintsK]

In newer firmwares it is possible to switch off EGO correction below desired MAP.

[ranz]

In newer firmwares it is possible to switch off EGO correction below desired MAP.

The EGO correction is already off below 40kPa (Minimum MAP 40kPa @ EGO closed loop control settings).

[GintsK]

ranz, it was more addressed to Sprocket.

I never use both the pressure based and the RPM based overrun fuelcut at the same time. I prefer the RPM based one every time.
In this case, if you have to keep it,  maybe use 15 kPa or less, to make fuel resume at a higher RPM.

Anyway log shows fuel resume above configured KPa. 18Kpa configured 25 in reality. It is 0.72s delay and 900Rpm instead of quite good 1700.

[mattias]

A page created in Wiki for this problem :
http://www.vems.hu/wiki/index.php?page=MembersPage%2FRanzAudi

I also noticed the too late fuel resume and made the Wiki page because of it, even though this is hardly the problem in this case as he shouldn't have any problem without overrun fuelcut - which he obviously has anyway, most likely a tuning problem.

First remedy is, tune the engine without overrun fuelcut enabled. Set the VE table low kPa load sites to reasonable values. Not 16% as it is now, make it 75-85%. Raise until engine brake reveals a not-lean condition.

[ranz]

This problem seems to be solved now mainly, you just have to increase IDLE PID D to something like 150.
http://www.vems.hu/wiki/index.php?page=MembersPage/RanzAudi

[mattias]

Increase the integral to 50/50 (increase/decrease) and post a datalog of typical idle, slight revving, maybe driving in gear and release to neutral.

[ranz]

Increase the integral to 50/50 (increase/decrease) and post a datalog of typical idle, slight revving, maybe driving in gear and release to neutral.

I have apsolutely no idea what these integran numbers mean... I had them on 50/50, someone on other forum (maybe here... I don´t remember) sayd that this is too much and lower them
But as I said, no problem after changing D to higher value.