My 2006 650i loses power under moderate to heavy acceleration. If I accelerate from anywhere over 2500rpm, it will accelerate then the engine rpm will drop suddenly by 500-1500rpm, and then will continue to accelerate again from this lower rpm. It only seems to happen once each time I punch the pedal. The car does not throw any codes. I have had the dealer and Dinan Performance examine the problem and they have not been able to isolate the problem. They have run vacuum leakage tests, fuel pressure tests, and may have checked the throttle position sensor. Any help out there? This really takes the fun out of driving this car. I have about 50K miles on it.
I wonder if you have a partially plugged exhaust system.
Some BMWs have a thing called a DISA that sits in the intake manifold. It has a plastic door that changes position as the RPM changes to ‘tune’ the length of the intake manifold runners to optimize the manifold geometry for different RPMs. When those fail, they cause weird things to happen across the RPM range but generally won’t set codes. Try to find out if your 650 uses a DISA and if so, get it checked.
Similarly, a problem with the VANOS solenoid or seals can cause weird things to happen across the RPM range. 50k miles is pretty early to see VANOS problems, but stuff happens sometimes.
I have the same problem tooo did you figure it out yet? what I’ve learned that the car only does that when your not in sport mode wit traction control turned off .
The symptoms sort of sound like a turbo charger problem. Is this a turbo engine? If so, there’s a bmw tsb no. SI B11 12 15 that might help, dated 8.2015.