Car has hard time starting,?

1997 volvo 850r, true mileage unknown. Car has hard time starting, sometimes it fires right up and sometimes it takes several minutes of trying. When it does fire up, it runs beautiful with no issues. I am getting NO check engine light. So far I have replaced, plugs, wires, distributor cap, rotor, ignition coil, crankshaft position sensor, camshaft position sensor and I am getting ready to do fuel filter tonight (never replaced). Fuel pressure is good and all relays are ok. Somehow I doubt that the fuel filter is the problem but could it be? any other suggestions?