In reply to jimtitt:
I think it's slightly more complex in that the "fix" tries to get the emissions down to the original figures in-test, but not just by using the original software settings.
The impression I get is that VW have juggled the mapping so that when the engine is warm, and running at mid-high revs, there's no difference, but that at low revs (say up to 3000) and especially from cold the performance is knackered. Hence the amount of difference you notice will be related to driving style.
One person dynoed his car before and after - result below.
http://1drv.ms/b/s!AvcWk_HHJ7e2lSKCPGtHBV19b90L
VW are, naturally, ignoring the evidence.
I'll admit to being disappointed with VW. I thought they would be doing a better job of this.
Also, as far as I know, all this is about NOx emissions which are not part of the UK test. Hence an unfixed car will pass the UK MOT fine. That's not the same in the states, where I think they do test for NOx hence the difference in treatment.
As far as I know apart from pressure from the EU there was no legal reason for VW to fix European cars.
The story I heard was that the Environmental pressure groups in the US sucessfully lobbied for a reduction in NOx to a level that was not achieveable in the timescale without an entire engine redesign. Companies that were in the process of designing/releasing new engines were fine - they could incorporate the changes, but VW had just released their new engines - and were not scheduled to update them for several years.
VW were then in a fix. They could either recall hundreds of thousands of cars and replace the engines with engines that didn't exist, and hadn't been designed (bearing in mind an engine design can take a few years from drawing board to car) or fiddle the test for the recently released engines and rapidly start work on a design that would pass the test legit for release in cars in a few years.
All was fine unless someone noticed, and as emissions tests were not a hot topic and no-one really cared (a bit like the "official mpg") there was a good chance that as long as they could keep it quiet for a few years it would all blow over.
So to a certain extent there is a blame to the legislators who pushed NOx emissions into law in a timescale that was not achieveable by the auto industry without a huge hike to car prices.
Incidentally, I know that this is open house on VW bashing, but as most other manufacturers were doing very similar (Mercs simply turned off most of the emission controls after a time period slightly longer than the standard emission test), I think they are mostly as bad as eachother.
Post edited at 10:01