ETS light is on with non of the common symptom.
No hunting, stalling or surging. Idle is perfectly steady.
Any ideas?

1999 S70 AWD, 130M miles.

 

I am curious about this too. I also have ETS light comes on and off without any problematic symptom typically known to be related to ETS.

Mine is 1999 S70 T5 91K miles

 

There seems there was a recall for this, but the free fix time may have expired (10 years.) Was the software updated on your vehicle?

 

I am not sure about that actually. I just got my s70 T5 a month ago, and I know the previous owner who sold me this has never visited dealership. Of course, she was not the first owner. I just opened the hood and looked at the ETM. It has a yellow sticker on it with "Magneti Marelli".

 

I called nearest dealer, and they told me that mine had software update in 2006. They also said that they cannot find the record of whether my unit was replaced or not, however, it is most likely so if there is yellow sticker on it. So, I guess mine is the latest ETM. My only symptom is when the ETS light is on, cruise control does not work. And ETS light typically comes on when it is cloudy or rainy. I don't have a rough idle problem as I see on youtube clips. I don't think the car runs with decreased power when the light is on. It always runs fine after the ABS problem is gone. Could this be some thing similar like ABS module problem, the bad solder joints?
Anyway, after some googling my only option seems to be sending it out to Victor Rocha.