I'm new over here on Bimmerfest but am on a couple other forums. Happened to see the thread here and decided to join and comment on the OP's issues. My car's an '04 545i with 79,000 on the clock.
A little background....I had an oil stain on my garage which I ended up figuring out to be a cracked transmission pan. Brought it into dealer and had them replace that, the mechatronics sleeve and the trans. fluid.
After doing all this I had the same exact issue as the OP. The car would shift into 5th gear and then between 35-40mph at a very low 1200rpm or so I would get the surging or slipping of the transmission. It was a very light repetative hesitation. It almost felt like the electronics were trying to decide whether it should stay in 5th or shift back to 4th because of low rpm's. It would happen with an extremely light accelerator pressure. If you gave it a little more gas it would go away. A couple times I'd get a really harsh surge almost like the "slam". It would never throw a code.
I brought it back in and my tech drove the heck out of it and couldn't get it to do it. He reset the adaptive values and the thing ran great getting home but next day the slip was back again. Took it by my tech house, drove around for 20 ins. and you guessed it....nothing!
Back to the shop we go. He opened a case with BMWNA and phone tech eventually isolated it to the mechatronics unit. BMWNA agreed to warranty the $3,000 part and I have to cover the labor at $780.00.
Hope this helps others. It seems like it's becoming more and more of an issue. While I did get the part fully covered I'm not sure how much goodwill they'll extend to others. It seems to be on a case by case basis. I also see that many are questioning the car needing to throw a code to get service to do anything. The code helps the tech opening a PUMA case with BMWNA. When it throws a code, the BMWNA phone tech can see it's thrown a code and can go into car's electronics over the computers and try to figure out the issue. It really helps your local tech deal with BMWNA in expressing exactly what is happening.
Last edited by Ben's 545i; 02-05-2010 at 06:22 AM.