RPM hangs at 2500

[marches]

Porsche 911 - 3.0 - EFI ITB - Slightly aggressive cams - StormX - new build

Car is still running rich, working on refining the master fuel vals and fuel table.  Finally have Ignition Idle Control behaving most of the time ( no idle control valve ) but have seen where the motor hangs at ~2500RPM and will not go lower until load forces it to around 1900 or so, then Idle Control seems to take over.  Below is a screen grab: Motor is warm and is at idle, then a blip of the throttle sends RPM past the critical point and it hangs at ~2500 RPM.  What is causing this?

Also, I notice sometimes at cruise, it seems the idle control is trying to interfere as exhibited with a retard of timing, when ideally during cruise, the config would remain more static.  I imagine if I had a speed input, that could be configured in the Idle Control settings to prohibit the Idle Control algorithm interfering while the car is in motion, however, what if I am at cruise and am almost to the exit ramp and want to shift out of gear and coast to the stop?  

Assuming this is coming from my ignorance of Idle controls...  Any hints from the braintrust?

This link includes the current tune and log file used in the screen grab above:

https://drive.google.com/drive/folders/1r8Ov-H4WvwATwXLDTlLCQjBqWIwvCeTC?usp=sharing

Thanks folks!

m

[Adamw]

Even with your ignition timing at 0 your idle speed is 200RPM above target, when you touch the throttle, idle ign control turns off, advance returns to normal values so the RPM jumps up to a value higher than your lockout.  

So, it appears your throttle is open too much, you would normally aim to have the idle RPM sitting on target when the idle ign is sitting on about the target.  

For the problem with idle ign interfering with cruise, this is the main reason you normally have a speed lockout.  But you may improve the situation by dropping the TPS lockout to 0.5% so idle control disables with the slightest touch of pedal.  

[DerekAE86]

You also have the RPM Lockout set to 1250rpm above the idle target.
So at 70+ degc your idle target is 1138rpm. This means idle control will still want to engage all the way up to 2388rpm.

If you cruise at lower than this engine speed it'll always kick in when your TPS% drops below the TPS lockout.

[marches]

Thanks Adamw and DerekAE86!!  

RFTM: RPM Lockout...  I foolishly plugged in 1250 assuming was the target RPM, silly.  Details matter!  Thanks!  Also, I am sure adding a speed sensor would help clear matters up.  However, lowering the RPM lockout to a reasonable level has stopped the jitter at cruise, no surprise!

The use ( abuse? ) of the ignition idle control is a result being at my wits end trying to get the idle to tame down without too much ECU intervention.  I have seen plenty of posts with folks frustrated with getting the ITB motors to idle without intervention and am still trying to get there myself.  I have spent some time making sure the butterflys are just at their seat, balanced them over and over and still the idle, without much ECU intervention, is ~2K.  Per an oft referenced writeup by jpnovak ( of pcar fame ) I made an 'idle well' in the ignition table such that in the idle range (1K - 1.2K, TPS 0 - 1 ) the ignition is 8 degrees BTDC.   A little more reading this evening suggests that a motor with a 'bigger' cam may require a little more air, so maybe the butterflys are too tight at close.

Could be as simple as too much fuel in that range?  Will experiment with that this evening!  

Thanks again!!!

mc

[DerekAE86]

Adding in a good idle control valve or converting to a ethrottle motor to open your ITBs will make sooooooooooo much difference to your idle quality.