Kainalu

Hi all, I just moved from Hawaii to the Bay Area with my 2006 530Xi wagon (E61) that I bought "BMW Certified" in 2010. I have had several issues with this vehicle but mostly with a good outcome until now. My problem is while driving, RPM's drop about 2,000 in a split second as if i slammed on my brakes then bounce right back to where it was. This usually happens while driving over a dip in the road (down), i.e. asphalt to concrete or before or after an overpass but never while driving over a bump (up). Also the car has shut off power a few times when coming to a stop. I think during those times the AC was on (wife also drives). Thinking the AC had something to do with these problems, i always turn it off but it turns on on its own, spooky. Anyways, the AC doesn't bother me as much as the violent jerking or the car shutting off at a light so hopefully someone can help me with this. 2 BMW mechanics can't figure out the problems and said I have to wait until the check engine light comes on. I'm grateful for any positive feedback and thanks for reading!