2004 S60 2.4 non turbo check engine light

Hi,

I bought my `04 S60 2.4 with 143k this year and it`s at 161k now. Did oil changes, replaced spark plugs and an axle shaft and ran pretty nice so far. However I have the check engine ligh on for about 2-3 months and trying to figure out the reason. It didn`t seem to important until it stalled on the freeway about 3 weeks ago. I restarted it and never did it since. It has pretty high and rough idle when it starts up. (almost regardless if its warm or cold) Also if I don`t wait like 15-20 seconds before pulling ou of the garage it would give me a rough ride out.
I did a little research and started with cleaning the ETM but it was actually pretty nice and clean. Had a mechanic check the fault code and he said it was the fuel pressure regulator first and then the fuel pressure sensor.
Well before touching those I thought I would just replace the fuel filter however it seems to have the non-replaceble one that`s built-in the fuel pump. So I have to go with the fuel pressure regulator but I just can`t find it on this vehicle.
Anyone can help with it?
Or any other idea what could be the cause?

I also heard that a software reload on the ETM could help.

Thanks,

Balazs from California