tranny stumbles every 2-3 seconds when cruising

[TiAgX5]

Originally Posted by X5_Rob

I brought it to a very reputable BMW repair shop. They determined my alternator was producing voltage spikes and error codes.... apparently the transmission electronics did not like these voltage irregularities... they believe the torque converter and tranny are fine... .replaced the alternator and all seems well.. I'll update in a few days/weeks when I get some miles driven on it... As odd as it seems the alternator repair seems to have solved my issue...

It's a good idea to keep a voltage disply that plugs into the cigarette lighter in your vehicle. The X is hyper sensitive to alternator output fluctuation and this is a cheap way to see output in real time. $10 at Walmart.