Idle Timing starts to jump up and down on cold start when switching to D

[Fabian]

Hi there,
i got an 2010 L99 Camaro with an JRE LS3 conversion kit and an mild cam.

Mods:
ARH Headers, Fast 102 Manifold and throttle body, custom torque converter, aftermarket heads, 200 cell cats.

My car starts up great and also idles very constant at 800 RPM with solid idle spark in P or N. When i start the car in the morning and switch from P to D it starts to loose the constant idle timing and jumping up to 18° up and 18° down from where it should be while holding the brake pedal. It also bucks while holding down the brake pedal. After loosing the brake pedal it revs up a little then drops and is in solid idle and no problems any more. From this moment on i can put down the brake pedal and it will retain smooth idle in D. Its only the first time after the start when switching from P to D while parking and holding the brake.

Im unable to figure out what is the reson for the first bucking while in D and holding the brake pedal. It just behaves like that right after the start when i'm still on the brake in D. When i switch back to N or P the idle is smooth again. Wehen i switch back to D it start bucking. But as soon as i let it roll for the first time after the start for lets say 10 meters it also does not buck any more in D.

Has anybody an idea why the car is behaving like this?

Best regards
Fabian

[Fabian]

So after this morning i tried this afternoon a warm start.

The car fires up great and after a while i try to give the gas pedal a little goose, it revs up and then dies!
I start the car again and take it for a little drive, this time while i was switching fom P to D there was no bucking. So in warm conditions the bucking on a transition from P to D seems to be gone.

After a while i stoped and took it in to N and tried again a gas pedal goose, again it revs up and falls to low with the rpm but this time i was able to prevent it from dieing by goosing the gas pedal softly but without this action it dies.
Started it up and drove home. No problems when switching from D to R and then to P.

I already tried to add more final idle airflow, but then it surges and dies rigth after the start, also with less final idle airflow.

I do not have a clue while the car behaves so differently.

Does anyone of you has an idea?

I posted the log and my current tune.

Best regards

Tune:
Camo2010_1405215_lowIdle_2.hpt
Log:
idle.hpl