The single most important improvement to FE you can ever do. FREE.

[landspeed]

10,000 ft . I wish I lived that high up!. I suppose, it shows the value of 3 things for good fuel economy:

(1) Driving style
(2) Aero mods (if you can't thin the air, at least you can reduce the resistance!)
(3) Reducing pumping losses (again if you can't thin the air). Unless you can get new cams made, this will have to be be increasing the throttle load.

By the way, a simple way to think about the engine on + idling or 'coasting in gear' argument would be...

- The engine uses a certain amount of fuel to idle at 750rpm
- If you coast in gear at 1500rpm, the engine will be 'wasting' more energy
in the form of engine braking. This energy originally came from petrol, so, by coasting in gear at 1500rpm, you are wasting more energy than by idling in gear.

The only real reason to coast in gear would be to slow your car down, without using the brakes, because there is a red light / junction etc up ahead. This is more efficient than idling + using brakes.

Something I have noticed with my new lambda sensor - the brakes run on vacuum, so, at idle (with the car not moving), if I press the brakes 3 times in a row, the mixture goes to 20:1 briefly (because the brakes are using the vacuum by letting air flow from the environment into the inlet manifold). When this happens, the engine runs OK, maybe *slightly* unevenly. I know that you do get a lot of NOx emissions with lean running, but would this be the case at idle?. If not, it might be possible to modify the mapping so that, at idle, the car runs lean and uses a lot less petrol (noting that diesel engines run very lean at idle).