Just keep your foot out of it. Diesels are fuel throttled engines (unlike air throttled gasoline engines), the new Common Rail Engines run ultra-lean as it is during steady state highway driving, you control all fuel entering the combustion chamber with the pedal, the biggest impact on fuel economy is how you drive it. Get a Scangauge II and you can easily see this by monitoring fuel flow.
For example, I have a Revo tune (http://www.revotechnik.com
) for my car, it's good for an additional 45HP and 53 ft/lbs of torque and the fuel economy shows it when I request power (i.e. by putting the pedal all the way down), however if I drive normally, for instance on cruise control at highway speeds, the tune has zero impact on my fuel economy over the stock ECU tune.
Search the site here, there are several lengthy threads on the topic, search for "hypermiling".
'10 Jetta 6M Sedan, 35% Llumar tint, WeatherTech Floor Liners, TDIclub Plate Frame, B2, PS, ScanGauge II, Micro-Can VAG-Com
Last edited by tcp_ip_dude; December 7th, 2011 at 00:49.