Mine does something like that and I don't have bluefin installed, it's strange as you come off the throttle and the thing just accelerates again without any throttle Input!
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Boost pumping - a problem with early turbo cars -some early Audi turbos used to do this - there was so much lag the throttle did not seem to be connected to the engine and the car might "take off" just as you are lifting off the throttle
when you "boot" it it energises the turbo, if you lift completely off the throttle the ECU cuts the fuel, but if you are on part-throttle the energy/ boost is still "in the system" - its all about the engineers balancing, performance/ economy/ drivability/ lag etc
Other cars were "all or nothing" and the throttle was like a switch - full throttle or no throttle with no in-between - thats what turbo cars used to be like and we had to adapt our driving style to suit