The automatic tranny in my e39 540i is doing something weird. The other day, after about 30 or 40 miles of “highway speed” driving (70-80 mph), and then decelerating to speeds for local roads (35-50 mph), my car downshifted momentarily, then shift back to 5th gear. It repeated this downshift-upshift pattern three or four times over a 2-mile period. Each shift was pretty “jerky,” and only lasted a few seconds. It was as though the tranny couldn’t decide which gear it wanted to be in. However, I was not accelerating hard (causing it to downshift), and I feel certain it should have stayed in 5th gear. I parked the car and when I next drove it 1-1/2 days later, it shifted fine, even after a similar 30-40 mile run on the highway, then 5 miles of 35-45 mph driving on local roads. I had a similar shifting issue a few months back, but it was on local roads and it happened so quickly that I didn’t know if it had actually downshifted, or just had a momentary “miss,” or something. When it did the downshift-upshift action the other day, I saw the revs jumping as it downshifted, then shifted up, then down and up again. So I am certain that it was actually downshifting this time and not any “miss.” My car is a 2001 540ia with 126k miles. I replaced the original transmission with a rebuilt unit about 30,000 miles ago and the car always shifts normally except for the intermittent downshifting described above. I don’t get to drive my E39 very much; my daily, round-trip commute is only 10 miles, all on local roads. I am able to get it out on the highway maybe once a week, and get it up to highway speeds for maybe 10 miles. All service is up to date, including all of the usual oil-related items: seals, gaskets, etc. I have no codes nor idiot lights flashing. I seem to recall that this car may have some type of “adaptive” transmission, that adjusts shifting patterns to the driving tendencies of the operator. Since most of my driving is very local, with weekly short highway trips, I am wondering whether the downshift issue I am having could be “fixed” with some type of “flash” or “reset” of the transmission “memory.” Thank you for any help or suggestions. (Please skip the suggestion that I should have gone with a manual tranny. I would if I could, but it is not practical at this time.)
