I got the car in January 2002, so I have only been through 1 winter. (was that a real winter last year?) I think I can say that in Vancouver we do not get Winter diesel. At least I did not see a significant drop in mpg's in winter, or a significant increase coming out of winter into summer. What I do notice is a drop in mpgs during wet weather, the roads are wet, and puddl-y, can cause mpg's to drop by 5% or 10%. The fuel gauge I think is accurate to +/- 5 litres so its hard to tell sometimes!
As for the coke up of the intake, and dialing out the egr. I haven't done anything with the egr. The car now has 60,000 km on it.
At 40,000km I took a peek into the throat of the egr with my 1million candlepower sooper dooper lamp. Hey is was black in there! It looked like black velevet, but really matt black. The coating was maybe 1mm thick, was very dry and powdery, had a windswept appearance, little channels cut in the surface. I touched it with my finger and there was hardly any resistance, and my finger was coated with a very fine dry black powder, finer and blacker than anything else i've seen.
At 56,000km I took another look. This time the coating was black and shiny, and of no thickness at all. Like it had been smeared with this really black oil. I have no idea why there was such a difference, as the only thing I had changed was the concoction of my additives.
Since then, the car has refused to start twice. On both occasions it was right after I had turned the car round. ie backed out of the garage turned round and backed into the garage, basically ran the engine for 30 seconds, and drove 60 feet. Having loaded, unloaded the trunk, whatever, maybe an hour or so later the car refuses to start.
The culprit was the anti-shudder valve which had not re-opened. Just touched it and it reopened, and the car started again. So obviously that black oily residue inside the egr is having an effect on the anti-shudder valve, causing it to be sticky.
The other point though is that the story behind the blocked intake manifolds is more complex than is often being presented/discussed.
I think I read on this forum about a Vancouverite who had a blocked intake at 50,000km. (?Petrolero? -not sure) That car was driven with some revs and still it blocked up, and at a relatively low km. So go figure. he was using Tempo fuel, and Lubro-Moly additive, if i recall correctly.
hth
cheers,