Help! My 2001 540ia is running poorly and I would like to get input from club members before I visit my indie BMW mechanic on Monday. Facts: (I am providing a good deal of detal in the hope that something I write will help provide a clue to one of you.) My 540ia Sport has ~98k miles on it. I purchased the car about 9 months ago as the third owner. The car has been well-maintained and all of the "regular" stuff (eg. valve cover gaskets, radiator/water pump, normal maintenance) has been done. About 3 mos/2k miles ago, I decided to do the one mainteance item that had not yet been completed: replace the lifetime tranny fluid. So last weekend I replaced the automatic transmission with a professionally rebuilt unit. (I will skip the painful process where the old tranny with the new fuld started slipping a few eeks ago.) In any event, the new tranny was installed by my brother (a Benz tech) and his buddy (a former BMW tech) at a Benz shop. (Pleanty of knowledge, all standard shop tolls, limited BMW "special tools" and no BMW computer.) The tranny swap went relatively smoothly. While they were in there, they replaced the weeping rear main seal, crossover gaskets, etc. To my delight, everything went back together with no left over parts or fasteners and my E39 fired right up! We topped off all of the fluids, warmed the car, re-checked the fluids (including the tranny fluid), checked for leaks, road tested the car and put it back on the lift to check everything again. No leaks, no check engine codes on the dash and no problems noticed. I drove the car this week and it seems to run and shift fine. (The new tranny appears to still be "learing" and adjusting shift points, etc, but overall is doing fine.) The other day, however, I noticed a "stumble" or miss once the car warms up. The problem occurs at a steady 45-50 mph, when the revs suddenly drop from 1,500 rpm to about 1,100 rpm, and then go back up. I can't tell if the tranny is actually shifting or not as the revs bounce. The revs continue to bounce intermittently as long as I run at this steady speed. Once I speed up to about 55 mph, the problem seems to go away. The car does not report any codes on the dashboard, either. My brother/mechanic took the car back and re-checked everything that he could: No leaks, no obvious problems with the tranny work, however we still do not have access to a BMW code reader. I have reluctantly parked my car for the weekend and plan to take it to my indie BMW shop on Monday for them to pull the codes and trouble shoot the problem. In the interim, I would be VERY interested in opinions from any club members who have any thoughts on what could be causing my problems. I am thinking maybe the new tranny needs to be re-programmed. Alternatively, the "stumbling" could be completely unrelated to the new tranny. A fouled plug, bad boot or coil, or even water in the fuel or a bad fuel filter. Please let me know your thoughts. Thank you.
I believe it is probably unrelated to the trans. I think it is likely ignition system related, but that your indie should also leak test the intake system with a smoke machine.
Follow up: Turns out the "stumbling" was torque converter lock-up. Bad torque converters are fairly common on these ZF trannies. Car is at the tranny shop, receiving a new torque converter. No charge.
I suggest that you invest $99 in a Peake Tool Code Reader so that you can save yourself the money and frustration of always having to rely on your Indie since your Bro doesn't have access to a BMW code reader...just my .02. Did you ever solve the issue? Ooops...just noticed it was the torque converter. Good catch...