that RPM range is the Large DISA open point do it has to be something about air flow.
- Throttle body malfunctioning @ that point
- Valvetronic map enters a new stage at that point, due to new DISA state. Since when tuned it was worse, this could be it.
If you have a shop & time. Maybe take off manifold, connect Throttle body on its own on the side and rev the engine. You should see Throttle body opening & the valves opening. Like the n52 530i youtube video w/out manifold
Although this is alot of work only to see flaps move...
128i Sport 6MT converted to Euro 130i spec, tuned by evolve ~220 whp 207 wtq(ft-lb) SAE
In-progress: e46 m3 trans mnt, e36M lip Wishlist: m3 susp, n55 eng mnt, headers, LSD, finn dif e60
"The 1-series is the last car that BMW engineered before the Germans, as a car-making culture, fell out of love with driving." - R&T 2013 135is