First pic
JDM D15B vtec idle and engine bog down problem.

Idle is real shaky and when throttle is blipped engine bogs down. When vacuum for Fuel Pressure Regulator is disconnected it idles good and doesn't bog down when throttle is blipped. Pressure Regulator is good, even adjusted it down a bit but still same problem.

Done test as per first photo and everything is fine.

Second photo, Don't know how I got onto googling it, but googled about signs of blocked/partially blocked fuel return line and I have some of the symptoms.

Is it worth blowing air through the line to see if anything comes out?

New 255lph fuel pump, new adjustable fuel pressure regulator, tested TPS and map, tried another intake manifold with another throttle body, don't see it being a vacuum leak as basically all of the lines have been replaced.

Not sure what else to check, have had this problem for ages and have checked over so many things.