Hi all,
I've researched this issue and found out it could be a dirty MAF sensor, so I disconnected the MAF sensor and started the car but the idle remained rough. I've read that cleaning the throttle body helps so I got CRC throttle body and air intake cleaner but on the bottle it says not to use on turbocharged engines? And I have no idea where the throttle body on the S70 GLT is anyway...
What else could it be?

 

Do you have a CEL?

 

Nope. But speaking of, the lightbulb light turns on whenever the brake pedal is stepped on

 

That means you have a brake light bulb out.

You have a '99 so you may have a bad throttle control. They go out a lot in those cars. If you do not have a cel, you are likely not missing.

 

What do you mean not missing?
And thank you for the brake light answer, very helpful

 

Missing means that one of the cylinders in your motor is not firing. That is the most common cause of rough idling. You have 5 cylinders and if 1 of them is not firing, it will cause a rough idle. How many miles does the car have on it?

 

Approximately 120k.
I might also add that the car dies every now and then while driving, usually during stops.

 

https://volvoforums.com/forum/volvo-...-stalls-55928/

In that case, try this first. Fuel pump relay.