My ZHP exhibited the problem long after replacing the DISA with a brand new one. The DISA doesn't even open up until 4000 RPM, so I seriously doubt it's the cause of this particular issue (it probably did contribute to the infamous 4000RPM dip however). Software update was what finally fixed it
Originally Posted by flashmeow
The problem for the ZHP "stutter problem" was two main issues: DISA and KNOCK SENSOR.
The older DISA would make a loud noise when the DISA flap gets activated. As a result, the knock sensor would retard the timing because it thinks there was actual engine knock. the solution that BMW came out with was to update the DME and to release a different DISA.
I hope this helps. good luck!
Last edited by TerraPhantm; 01-20-2013 at 11:10 AM.