Exhaust Back Pressure at Idle . Turbo boost spiking

[Rawze]

(11-28-2022 )BrandonOlsen Wrote:  X15 CM2350 X114B
Having exhaust back pressure at idle. Doesn’t matter if engines cold or hot. At 700 rpm it’s not very noticeable but you can hear the turbo boost intermittently. At 800 rpm boost goes up to 10. At 950 goes up to 20. When idle reaches 1000 it goes away. ...

I don't see an issue with your post much, other than your likely just chasing ghosts.

There are 13+ different engine operating modes inside that ecm.. and if the DPF, SCR unit is not close to 500+F.. then the engine will choke the exhaust manifold + create a bunch of internal engine friction because it has gone into one of its aftertreatment "rapid warm-up" operating modes. Weather and altitude effects this too.

-= The EPA requires the engine to pass emissions as soon as possible after it is started up,.. and it cannot do this until the cans under the truck are up to temperature... hence the different operating modes.

This is also why it will randomly spool up and down the turbo when driving on flat ground.. it is regulating those cans under the truck... changing engine operating modes every few mins sometimes, depends on how cold, etc. it is outside, to do so.

as the system ages.. and sensors read differently over the years the engine will act differently too.. so if you have not done a recent EGR tune-up on it.. then that is the place to start.. and at 600k miles, the egr cooler is likely not flowing as well as it should.. might need to clean it out too.