I noticed in LFS when you press 'I' to shutdown the engine you can still hear it running, pressing the throttle has no effect on the car but still generates some noise. Just a minor issue which hopefully can be fixed when realistic engine ignition is implemented.

I'm guessing you are just hearing the wind noise. Not wind from driving the car, but there is actual wind blowing. I've never heard the car after shutting down the ignition.

When the car is stationary you shut down the engine and no engine sound can be heard once the rpm is down to 0. But while the car is moving you can hear the engine and throttle still generates a noise. Should there be engine noise when there is no ignition at all? Right now shutting down the engine by pressing 'I' is more like simply cutting the throttle. But then the engine ignition along with some other engine simulations are not yet completed, so maybe this minor sound issue will be addressed later too

any car with carb based throttle will prduce a louder more open noise when the throttle flaps are opened with the pedal down when the engine is turning, regardless of the cylinders firing,

this is because it varies the amount of resistance to air being sucked in, and as such changes the noise.

it's correct, but odd if you've never heard it in real life, I can make a video of this on my motorbike if you would like.