Sticky Wastegate?
Worth testing the Vacuum system with a mitivac as mentionned earlier. This is a good DIY:
http://www.youtube.com/watch?feature...&v=80TYILifxy4
Not sure the readings will be the same with Cobb though as the JB4 controls the vacuum to the wastegates more directly.
Otherwise, its time to get the DP's off to take a look at the wastegates directly.
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Car: e91 330d with Viezu map
Gone but not forgotten: 2010 Jaguar XFR (Cat-back exhaust, pulley, intake mods and map), Highly Modified E90 335i LCI M Sport Manual (circa 480BHP/500lb ft)