Alright guys,
I need some help... I have been pulling my hair out on this one for a while and I can't seem to figure it out...
I have a 2012 L96 6.0L out of a Sierra 3500HD. Cold air intake and Long tube headers. No cats, no post cat o2's. It has a manual transmission currently, but still working on buttoning up the detail work like the VSS. New o2 sensors.
My issue is.. During open loop after resetting the Long Term Fuel Trims, it runs just fine... A little slow response on throttle touches as expected, but besides that it will idle and run just fine. When it goes to closed Loop the RPM wanders up, then the spark will cut for a split second and it will drop the RPM some, but then it rises back up. Idle is never the same and never comes down to the requested RPM. There doesn't seem to be a reason or rhyme to it... I have checked for obvious vacuum leaks and I blocked off the two ports I know of on the stock manifold. I am open to checking specific areas again if someone has a specific spot to check, but I feel like it shouldn't be vacuum since open loop is just fine.
Here is my current tune and a recording of all idle with new o2 sensors.
2012 Silverado 2500 new 02 sensors 2.hpl
K2500_L96_Current_Tune.hpt
Any help would be appreciated... Thanks guys!