COBB - SUBARU IDLE ISSUE ( Speed Density)

Hi Guys, i have pretty much completed a tune on speed density for a ej257 on cobbs atr platform, howevere there is an issue that i have beentrying to sort for about a week now.

When you blip the throttle below 2k rpm it will miss the idle point on decel (set at 900rpm) and drop to 600 rpm and almost stall.. The idle stability tables generally correct the issue after 1 or 2 cycles and will eventually return to the 900 rpm set point- does not occur in forced open loop or if you blip the throttle above 2k RPM.

So Far - Speed Density VE tables were all mapped out in forced open loop and this issue does not occur in this mode- however i want to make sure closed loop is active on this tune.

- Injector Data is from Injector Dynamics spec sheet ( 1050x) and map Sensor is OMNI 4 BAR

- I have adjusted COBB SD MAP smoothing values from 1.0 to 0.3 and this had no effect on this issue which had been suggested on other forums etc.

- Tip in enrhciments have been altered many times and have had no postive effect in fixing this issue

- Overrun fuel resume is set at 200 RPM above idle point ( 900 RPM + 200 RPM) and has not made any positive changes set up to around 1500 rpm.

- I have played with throttle / Idle airflow tables and set them to the idle airflow i am seeing when its idle is normal at 900 RPM ( 3.9g/s)

I have attached a log showing the drops to 600-700 rpm under light throttle there is also times in the log where you can see it return to normal idle with no dip-

( For the record if you switch the tune to MAF based or SD (forced open loop) there is zero idle drop and the issue is resolved - only in SD MODE closed loop enabled does this occur)

I have noticed the afrs drop quite rich 11-12 afr before the issue occurs.

Wow, I just came to ask pretty much the exact same thing however my VE is still a work in progress. The car starts and idles fine in open loop but once it switched to CL the idle becomes erratic until is dies.

I'm running a built engine with GSC S2 Cams and a Cobb Map. I don't want to sit at idle too long before the meat of the break-in is done, so really all I've tried is overrun and ensuring the VE is very smooth around the idle MAP and RPM, that seems to help a bit. So quick reading has pointed to perhaps a bit more throttle angle at idle. Sounds like you've put a bit more time into it than I have. Good to know there is someone else out there dealing with the same thing.

Send me an email if you want.

jordierobb@gmail.com

Another thing I though of is the Load Determination Smoothing. By Default this is set to 1.0, or no smoothing. Cobbs SD guide indicates that in pure SD mode, no smoothing tends to work best, but also mentions there could be condition such as idle or tip-in issues where this setting can be modified.

I have tested multiple Values in the Load smoothing as you suggested and also mentioned in opening post 0.3 - 1.0 neither have sorted the issue. I logs i noticed the IDC goes to 0% when it returns to idle normally and keeps injecting when it goes rich and drops the rpm - 2k RPM is a threshold where this no longer occurs and above 2krpm the idle will return normal and the drop does not occur. Its seems to be related to the RPM Delta % when the throttle is lifted- i have tried adjusting the tables that cross reference this ( Eg idle stability tables) but has not resulted in a positive fix as of yet.

As for your issue Throttle tables - Throttle airflow minimum and target airflow tables should be enough get your car running at idle have used these tables effectively on another cammed ej257.

Sorry, I completely missed your mention of the smoothing tables.

What direction did you go with the Throttle tables? I added some angle last night at the lower idle airflow levels, but may have got a bit carried away because it wanted to idle at 2000 RPM once the car got over the 4 KPH. So I decreased the amount I added by quite a bit. I also added 2 degrees to the idle ignition for a total of 17. It was able to idle ok at 1200, but was still sensitive to load changes. I'm going to try adding a touch of fuel at idle and see how that helps.

Sorry, Didn't mean to hijack your thread.

Cheers,

Jordie

Just thought I would post the resolution to my issue in case anyone comes across this thread. I didn't notice that my injectors where hitting the lower PW limit when trying to idle at 950. I added fuel and selected a more reasonable idle speed to keep the injectors about .450 PW and it idle well now.