Perkins 1706J-E93TA Operation And Maintenance Manual page 51

M0087475-03 51
Operation Section
After Starting Engine
Extended Idle at Cold Ambient
Temperature
The engine may automatically change speeds when
the engine is idling in cold ambient temperatures
(typically less than 0° C (32° F) for extended periods.
The purpose of the automatic speed change is
threefold: to maintain the desired operation of the
NOx reduction system, to maintain the desired
operation of the regeneration system and to keep the
engine coolant warm. The engine speed may rise to
1600 rpm for as long as 20 minutes.