Quick question about going down hills...

[LincolnW]

I have been searching around and can't seem to find the answer to this question.

When going down hills is it more efficient to leave the car in gear and engine brake, or put it in neutral and coast down?

I am not quite to the point where I feel comfortable turning the engine completely off so I want to figure out the most efficient way while leaving the engine on.

I remember when I used to have a wideband o2 sensor in my car the air fuel ratio would skyrocket when I was engine braking (it would read so lean that it would go off the chart). But when I was coasting in neutral the engine would idle around 14.7. So it seems to me that I would be using less fuel if I left the car in gear and rode the gear than if I put it in neutral.

I assume this has already been covered time and time again but I couldn't find a thread about it so if someone could post the link that would be excellent!

Thanks!