I have a stutter that comes on at 2600rpm and lasts to 3100rpm. And a noticeable stutter while cruising at 3100rpm while maintaining speed. Similiar to a missfire feel. This is an 06 JCW. As of right now the stutter seems to have gone away for the most part but I don't care much for the fix. The dealer had me drop down to 89 octane. So far the car seems smoother but seems a little less peppy and the gas hand has dropped further than normal considering the amount of miles I've put on. I've yet to check the mileage but will in the next few days when I fill up the tank.

I have the latest software update as well as changed out my BP valve for a DT BP valve. Nothing fixed it until I drove over 100 miles with 89 octane. Would an aftermarket ECU update correct this problem? If so, besides MTH, what is available out there for those who can't get to a local shop for a custom programming?