6HP19 fluctuating revs

[Samach]

Hi, I have an issue with my automatic transmission. The revs go up and down when I am going on a constant speed. Can anyone let me know please if it's a torque converter or mechatronics issue? or something else? Thanks

Here is what it looks like:

[e91Owner]

The first thing to do is to scan for codes with an OBD scanner that can read all of the BMW modules.

[Samach]

Originally Posted by e91Owner

The first thing to do is to scan for codes with an OBD scanner that can read all of the BMW modules.

Scanned it and apart from exhaust back pressure sensor fault, nothing. My mechanic told me its a torque converter issue. Replaced it yesterday and the problem still exists

[Samach]

Just going to share some more details incase someone can help.
1- Car idles fine. No bouncy revs
2- Only happens under steady load (No acceleration or deceleration. Foot steady at the accelerator pedal) . When I accelerate, revs don't bounce and the TC does not slip
3- Does NOT happen when cold. Only when the engine is slightly warmed and so on
4 - Current faults are 1) 41BB-exhaust backpressure sensor and 2) 4A74-LIN/BSD Preheating control unit:Missing

[E90dima]

Might be a small vacuum leak, smoke test your car.