Volvo S90 transmission loses torque shortly after started

[kolev]

Volvo S90 1998 at approximately 140k was driving normally when suddenly started losing power meaning RPM would rise without creating usually expected torque.

My first thought was of a spark gone bad, but that wasn't it.

It quickly got worse to a point a few miles further of almost being unable to move from a traffic light and then it felt like slipping transmission. It barely had any torque on any speed.

Car entered winter/limp mode, but that was a result, not a cause of the problem, which I was able to confirm later through experimenting.

The syndrome was and remains a relatively short time during which there is torque after the car has started.

Trany fluid was flushed and replaced without any apparent change in behavior.

The odd thing is that as soon as the car is stopped and started again, even in a flash, the torque returns for a while, which rules out the usually suggested gear shift sensor or neutral sensor or whatever.

Once the car enters limp mode it requires resetting, of course, but the problem with the disappearing torque appears regardless of the startup mode.

Engine error codes are P0740 appearing first and eventually at some point (if driving) P0733. Water temperature is rock solid.

What I am looking for is a good theory on what is causing the effect or, of course, someone who has had the same and did not end up replacing the whole transmission. I am rather certain it will work if I replace it, I just want to know that I need to replace it as opposed to , say, replacing an externally located solenoid somewhere.

Finally, another thing I noted in many forums is how people do not follow-up to their own posts with what eventually they found out or what worked or not.

I can't bring much value to this forum, but I promise to at least follow-up with the resolution that worked or did not work for me.

As a first feedback I will say that a Volvo expert said radiator may have ruptured mixing coolant and transmission fluid and while the oil seemed normal at the probe, the antifreeze didn't so in one move I replaced the radiator and flushed the two systems. Nothing changed in regards to the original problem and I am not 100% sure the radiator was *indeed* broken.