More or less. But fuel consumption alone is not the only factor. Cranking up a diesel locomotive needs a really exhaustive set of checks to be performed, that usually takes 15-20min if no issues pop up. And this process is also very intensive, so the LPs would want to avoid it by idling the loco for short rest sessions. In addition, it will consume much more fuel to start the loco if the engine becomes very cold (Due to the way the combustion and the fuel work), so particularly in cool weather, it is preferable to keep the diesel locos idling than shut down.