FWIW, one sentence in the USA Today article linked to below suggests that it is not yet clear as to whether a software fix will lead to worse consumption/CO2 values and performance: 

Quote:
"It's unclear how the fix will affect the fuel economy and general performance of the cars involved in the scandal, though some industry experts expect the cars' fuel economy ratings to fall."

http://www.usatoday.com/story/money/cars/2015/09/29/emissions-scandal-volkswagen-propose-diesel-cars-fix/73028188/


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fritz