High Idle On 2015 Cascadia

So I've heard from a lot of places that it's bad for your engine to idle at normal speed (~600rpm) for a long period. It even says in both the cascadia owners manual and the Detroit engine manual that you should idle at a minimum of 900rpm (or maybe it was 800, don't remember) when idling for an extended period. I have a 2015 cascadia with a dd13 and 10 speed manual. I've looked and looked onlineb and all over the cascadia and Detroit manual about how to activate high idle or fast idle whatever you wanna call it and can't figure it out. I've tried turning cruise on, hitting set or hitting res and nothing. Tried with brake applied, with range splitter up, even tried it while holding the rpm where I want it with the accelerator pedal. Nothing. Interesting thing happens though. When I hit set or res, the accelerator pedal no longer does anything. You can put it to the floor and it just sits at about 600rpm. Is it just not possible on this truck or what? It's a company truck so I don't care about fuel but I do have mechanical sympathy.. I don't wanna ruin a good engine regardless of who pays for it.

 

Tried it. Doesn't work.

That has to be it. Seems pretty stupid to me, then again I guess that's why my company gets rid of their trucks after 3 years. Also why the new ones all have opti-idle too...