Lots of misinformation here. "Computer" diesels engines should not be idled for extensive periods as it causes excess fuel to "wash" down the piston liners causing excess wear. Most manufacturers will recommend not more that about 3 minutes of idle time. If for some reason you need to idle more it should be bumped up to fast idle. The books also tells owners the engine does not need to be "up to operating temp", but usually off the peg and warming up before highway speeds. That usually means one can move out of an RV park spot as soon as the air pressure is up. Anyone trying to idle to get to operating temp or idle longer than required to air up the suspension is abusing the engine.