[euromodder]

First off - you won't get 900 miles out of a tank without some serious hypermiling effort.
The automatic transmission isn't helping either.

If the engine isn't reaching its proper operating temperature, likely due to a faulty thermostat, it'll use more fuel.

Though some disable the EGR valve , or put in a plate with a smaller hole as a restriction, it reduces fuel consumption during part-load conditions in "normal" driving conditions.
So, if it's not working properly, it can increase your consumption.
The exhaust recirculation piping can clog up with tar like gunk, or the valve itself stops working / gets stuck. Or both.


If you skimp on TDi maintenance, they tend to bite back in due time.