Check the fuel pressure, its the easiest way you can make sure everything from the pump to the filter and regulator are working correctly. If you are careful you can even do it with a tire pressure gauge on the test port.
If that's good then start looking for plumbing leaks. If there are none then it could also be a bad MAF or MAP sensor as well.
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2004 S60R - 350+ HP, AWD, Custom FMIC & Exhaust, Active Suspension & A Big Set Of Brembos
Crazy Camber, Stretch & Poke; its the new triple-stack-bleacher-wing ricer fad that's all the rage nowadays, lol