I agree with fuel pressure problem and to replace filter as first step. Sounds like it would be a good idea to replace filter regardless if you might need a fuel pump or something else. And I agree that after replacing the filter the next step should be measuring the rail pressure. No money wasted by replacing the fuel filter especially if it's never been done but going any further without checking the fuel pressure might not be a good idea.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)