6 months ago, the car started developing a surging after 2600rpm. Smooth as butter at any throttle input up to 2600, once past that point it starts to surge. Full throttle it is not noticeable but if you are at 40% or more throttle, a very noticeable surging starts and continues up to near redline. It feels like the throttle is going from 40%-70%-40% every 1/4second.
No codes.
New fuel pump, fuel filter with reg. Rebuilt Vanos. Car had latest flash in the DME but we reflashed it anyway, no change. Unplugging vanos seems to change the frequency and make it less noticeable. At that point I rebuilt the vanos thinking that was the smoking gun. Well it improved but is still noticeable. Car has 120k miles on it and auto trans. Torque converter seems to lock up normally so I don't think it is the transmission.
Replaced the injectors, DISA, Throttle Body, Smoke Test, New o2 Sensors, Guibo, Driveshaft support bearing, even updated the trans software.
Any ideas or suggestions would be awesome. It's my wife's car and we are ready to sell it but I'm not passing the problem on to someone else.