Weird Torqueconverter behaviour (98, Z3 Coupe, EU, M52B28, A4S310R)

[djmhendrix]

Some days ago I noticed that my torque-converter was not working as it should be. It is supposed to lock above 80km/h (~50Mph) when cruising with light pedal pressure. Now, it doesn't lock anymore when I accelerate with ease beyond that speed. However, If I push the pedal beyond the point where it would normally have released the TC lock, it now actually engages the lock during the ensuing acceleration. It is also noticeable when on cruise control (non-TU so regular servo on same throttlecable) and going uphill; it will accelerate and at what seems like the usual point where the lock would let go, it engages. Even when I push the pedal down to the point of Kickdown, the TC will be locked instead of released. If I actually do a Kickdown, it disengages and does the normal Kickdown stuff.
Think this guy had the same issue but that thread is very old so I assume there are no survivors....
I am sure it not ATF level related; all other shifting and torque is perfect and like it has been for years. DIS, INPA, Scanner 1.4.0 and Carsoft don't know what it might be.... no fault codes.
Who knows what this is?

[djmhendrix]

It gets weirder; I used INPA to operate the solenoid yesterday evening in the garage; in this test, it went to go turn itself on and off every 1-2 seconds. It continued to do so until I turned off the ignition. Left it like that and when I got on the highway this morning, for a minute or two, it seemed to lock like it should. However, after another minute or so, it disengaged the lock again and continued with the weird behavior.
Next try when I get home tonight: clear EGS adaptation values...
(logging my actions here for prosperity...)

[rf900rkw]

The problem with the 4L30 is it doesn't have a turbine speed sensor. That means all diagnosis has to be done by looking at the extremes, engine speed in, road speed out. You can not isolate The TCC function from the transmission gear function; making it hard to tell if you have a converter that is not locking properly or a 4th gear slip. Monitoring the TCC command while it is malfunctioning would be a useful step. Clearing the adaptions won't, as they won't effect this and there really aren't any on the 4L30 for the same reason, a lack of speed sensors to tell what's happening.

[djmhendrix]

Thanks for that knowledgeable review!
would it help this diagnosis that when the lock does engage, I get "full pull" in fourth gear without any slippage; it actually still accelerates quite nicely even.
I checked the throttle position sensor signal which was nicely linear in line with the pedal movement. I could imagine that the engine load is not correct but I doubt it because the engine purrs and roars like it should (perhaps a wire...?) Will try to take the INPA laptop with me in the car tomorrow...

[djmhendrix]

logged my data; seems my Mass Air Flow is fixed around 1150 Kg/hr.... doesn't move much up or down. Guess I will try to clean that friend first....

[djmhendrix]

Ok.... If someone else ever gets this thing.... Look here: https://workshop-manuals.com/bmw/3_s...0_310r_(thm-r/