Rs2 fuel pressure issue. Rather strange

[gutya]

Hi there!
I came across a strange issue with fuel pressure. With the vacuum hose connected to the fuel pressure regulator I have readings of 3.7kPa. When I disconnect it the readings ruse to 4.2. Thought the regulator was faulty and replaced i with the new one. The problem still remains. Correct me if I'm wrong - but I have always thought that the reading should always correlate with the one marked on the frp - in my case it has the marking of 3.8 bar , so the pressure should be 3.8bar in the ramp with the vacuum hose off. What seems to be the problem?
Thank you in advance for your answers. And pardon my English.

[Bowie69]

The vacuum line is there so at idle the pressure is lower so the injector timings can be better managed -it is not faulty, it is working as described, perfectly

[gutya]

Much appreciate your concern. The problem is the fuel pressure at idle with the vacuum line attached is too high - 3.9 instead of 3.5. What is target value at idle? 3.4-3.5 I suppose