Having a nightmare of an issue hopefully someone can help me rectify. Car is a 2006 BMW 550i automatic with 97k miles.

Problem: When coming to a stop the car shifts weird, dips below a certain RPM and stalls out. This is EXTREMELY dangerous as I lose all power...steering, brakes, everything! So if I slow down to make a turn, as I'm turning the car will just stall and I will be coasting towards whatever I'm aimed at with no power function whatsoever. It does this non-stop! Can sit, idle and drive for hours perfectly. It only does this on deceleration under 10mph which happens to be every single time you slow down.

History on car: A few months back previous owner had a full rebuild of the engine done. I'm talking all seals, oil pump etc etc to the tune of $5,000 plus! After doing all the work they traded it in because they couldn't figure it out. Unfortunately I bought it at auction and the seller stated it drives perfect and was listed as is due to miles which is typical for cars over 10 years old at auction. So I had no idea this was a problem until after I bought it.

Other possibly related issues: The lower gears seem to hiccup when decelerating at lower speeds. I've also twice now found the smaller vacuum line coming off of the vacuum pump split in half. I cut it back, pushed it on, it split in half again. I cut it back again and it hasn't split since. Not sure if it has anything to do with it, but being the bigger line of the vacuum pump leads to the brake booster I figured it may be worth mentioning since my car is having issues under braking. It also is throwing codes for the IBS which is odd because I have zero power issues with electronics and even if left unstarted for 5 days it starts fine. Lastly power delivery is not constant. Sometimes it has lots of getup and go, other times it is average acceleration at best.

My thoughts: I'm wondering if the IBS system could be the IBS failing or the alternator and creating not enough voltage? I was considering it maybe being the camshaft sensor as I've seen threads where other 5 series had a stalling issue because of them failing (although I don't have a code for camshaft sensor so this could be a far fetch)? Possibly the mechatronic system is failing and needs to be built? vacuum lines off vac pump bad?

I would really appreciate any and all help in figuring out this nightmare as this isn't just inconvenient but extremely dangerous.

 

I wish I could be of more help, but all I know is this sounds like a typical vacuum leak issue, I would have the shop who did the engine rebuild try to track down the source of the vacuum leak and go from there, good luck

 

When you say the car can drive for hours perfectly (which I'm assuming can only mean 100% highway cruising, nothing around town), that the very first time you slow down for a stop, it will stall?

Also, does this happen in DS steptronic mode as well as in Manual shift mode?

Have you tried driving with the transmission only in M1 mode (up to 10mph or even 20mph)? And allowing the car to come to a stop (or near stop) without using the brakes?

 

Any solution to this, as I am experiencing the exact same problem and occasionally the car will be completely electrically unresponsive. Including no response from the key fobs.

 

I would look into doing a transmission service. The stalling and strange shifts when stopping is usually indicative of transmission neglect. I did mine in my '08 550i, and that behavior stopped completely. I also went ahead and replaced the metatronic coil pack. world of difference. We never know how the previous owners maintained their cars. It could be the pressure from the transmission not downshifting or going into neutral properly is overloading your vacuum and making it pop off.