Hello, I own a Volvo S60 2001 turbo diesel and the problem is that when I reach 120km/h the car goes into limp mode, but when I slow down and accelerate again over the same speed while in limp mode it goes back to normal until reaching 140km/h and the same happens again. Sometimes when I accelerate really hard somewhere around 3rpm+ while in small gear it goes into limp mode too and I cannot go over 3rpm.
I have noticed that when I accelerate black smoke comes out from the exhaust too. I checked the engine fuses and noticed that the ETM fuse is missing, could that be the problem?

After restarting the car limp mode goes away.

Also, when it goes into limp mode - it shows a message that my engine needs service but no warning light, only the message.

 

If it is going into limp mode, you should have DTC's that can be checked with a scanner to lead you in the right direction. First step would be to have the car scanned. Some parts places do this for free.