Ghosting check engine light
 

New to forum..Wondering if anyone has seen this..I'm baffled.
2013 Mini Cooper S
I periodically get a check engine light indication (after the engine heats up and I get into the throttle). When this happens, I can tell that the turbo isn't performing, but I am still getting normal gas mileage, can set the cruise at 80mph, etc.. Acceleration definitely drops off, even with downshift. After shutting off the engine, when attempting to check fault code with OBDII, no fault codes exist. Took it to the dealer the first time it happened (with picture of check engine light)(knew they wouldn't believe me) and they have no clue...I replaced the blow off valve (my terminology, bear with me, I'm not an engine mechanic but can think critically-it only cost $78 for the part-still happens).
Turbo seems fine, no end float..no fluid leaks anywhere on vehicle. Air Mass flow sensor next stop? Don't want to throw money at a problem if someone out there has seen this already.. Thanks in advance!

Maybe drive it to the dealer or mechanic next time it happens, and don't turn the engine off? If the light is still on, they ought to be able to pull the code that tripped it.

That's the only thought that comes to mind at the moment.

Throwing parts at the problem is typically a very expensive way to not solve it.

--DD

Already did that..three separate times..'ought' didn't work out..