Did you ever sort this problem out? I notice a leak at the small rubber hose on the back of the fuel pressure regulator. The problems I have is that the engine stalls very intermittent.

If I understand it right there should not be any leaks at the rubber hose since it's just a precaution to lead fuel from the regulator back to the intake if the diaphragm breaks. And a faulty regulator will screw up the differance pressure between upper and lower chambers in the fuel distributor, hence the lean mixture (duty cycle ~30 %).

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'87 MBenz 190E 2,3 8vlv