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Factory tuning has an idle bump with a ramp down timer. At -20 F it will idle at 1350 rpm range for a minute or two and then slowly drop down to stock idle speed in the 700 range in a couple minutes. Linked with this ramp feature is a shut off when the brake/gear is selected.

GDE high idle turns on 30 seconds after the cold start and will ramp up to 1500 rpm stable until coolant reaches 160ish. The modified injection parameters push more heat to the coolant and reduce warm-up times by 50%...you may only get through a half cup of coffee and the truck will be warm. The first release of the high idle had a limitation, it takes some time to drop from 1500 to 700 rpm and we recommended moving from R to N To D with a slight delay in each gear...this helped reduce the potential for a clunk and harsh gear engagement. An update to this feature in February added a high idle shut off by revving the engine past 2000 rpm and letting off, then the idle will drop back to 700. Now there is no issue when shifting into gear.

1500 rpm provides better oil pressure through out the warm up.
Interesting. My 2017 tuned Eco with the fast idle (tuned in 6/18), when it's 36 F or less, ramps up to 1650 RPM's, stopping at 1300 for a minute. Has the high end idle been backed down to 1500? It does make some noise and warms up ultra fast, I like it! I can rev mine to return to idle.

Make sure to turn up the heater control.
 

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What's "high idle"?
Exactly what it sounds like. Diesels inheritantly cool off when idling. High idle is a elevated rpm to speed the warming the engine up. Normal idle is about 700 rpms, the factory tune will in certain circumstances raise the rpms to about 1100-1200 rpms, I GDE goes up to about 1500-1600 rpms
 
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