So in neutral it seems buses idle at a higher rpm than in drive. Would this be possible to simulate this in ror? Here's a vid for reference. TC/2000 FE Start Up - YouTube
1 min 14 sec in the video
This is a natural thing for vehicles with automatic transmissions, and has nothing to do with the high idle switch. When you're in neutral there's absolutely no load on the engine, but when you put it in gear you start spinning the torque converter which adds a slight load to the engine and causes the RPMs to drop a bit.
Unfortunately this is just one of those things that was never simulated in RoR's drivetrain code.