Generally, idle speed is kept at what range of rpm?

Idle speed is typically maintained in the range of 550 to 650 rpm for many heavy-duty engines. This range allows the engine to run smoothly while avoiding stalling and ensuring that necessary accessory systems, such as the alternator and oil pump, function effectively. Operating within this rpm range ensures that the engine is producing sufficient internal lubrication and adequate power to support various systems without straining the engine itself.

In heavy-duty applications, maintaining the appropriate idle speed is crucial for engine longevity and performance, as it provides a well-balanced operation while minimizing fuel consumption and emissions. This rpm range reflects the standard practices found in industry manuals and manufacturer specifications for many diesel engines used in heavy-duty applications.