small surge when coasting to stop, what table can affect this. log attached

[Gpargament]

I have attached a very small log that shows me coming out of speed and coasting to a stop. you will see the rpm's go from 1800 to 750 but then jump back up to 930 and then settle back to 650 where it idles. Is this a hysteresis delay between what sources are controlling the fueling? Any recommendations for eliminating that small surge? The car is an 07 c6z with SD tune, intake, headers and exhaust. Thank you in advance for any help with this.

small surge with when coasting.hpl

[Gpargament]

I have turned the maf back on and the surge is still there. now im back in SD mode

[lukearmstrong1990]

tune?

[Bearded Villain]

Not that you may have the same issue, but when tuning my wifes Envoy Denali i noticed a small surge/bucking on coasting (5.3/LH6, stage 2 cam), and i had throttle blade percentage acting weird when letting off the throttle, it would read 36-42% when i had no throttle applied. Cleaned the TB and performed a relearn, all was ok.

[Gpargament]

thank you both for the reply's, the idea of checking the throttle led to an interesting discovery. My throttle readings and sensors are correct, however when looking at the log for TPS voltage and position, i noticed the surge comes right after the computer switches from open loop to closed loop. Hence 2 questions is my car supposed to be jumping back into open loop? and what can affect the hand-off from one to another, is there a 50 RPM hysteresis, or a table that affects the computer choosing between open and closed loop?

I have attached my tune as well, its a speed density tune. I am not a master tuner(shocker lol) I will be gracious for any helpful advice

Speed Density.hpt

[07GTS]

your main spark idle area is a massive difference to the idle/idle coastdown spark when its going from throttle/driving to idle/coastdown tables its a big change in spark which would be noticeable as a dip its prob then having to correct for, also your adaptive spark coastdown/gear have values then the drop to zero so if any correction go too far underspeed it wont correct for them then the TB is prob trying to causing it to serge till spark is back within the rpm it can correct for

[Gpargament]

Freaking amazing my friend, I'll adjust those tables this weekend. I knew someone would know, again thank you very much

[07GTS]

ooh and it can be good in some to have the main spark always 8-10 deg higher then the idle spark for some reason sometimes the adaptive spark correction is limited by the main spark table so if u have it the same as the idle spark then it may not make corrections but if u have it say 10 deg higher it will then be able to use up to 10 deg increase to correct

[lukearmstrong1990]

adding to what 07GTS has said..... which will likely fix your problem with out any other corrections...… look at your DFCO exit spark. your DFCO exit spark is negative values which will cause the RPM to dip before that command decays back to idle spark table values. I often set DFCO entry and exit spark values to 10* to stop this

[Gpargament]

thank you to both of you, i never knew about the dfco exit spark and its effects, thats awesome and my z is running, coasting, and idling beautifully once again.