I have a 2005 Xterra that won't run. It will start but it sputters and the RPM's show 0. If I hit the gas pedal it dies instantly. I was able to get it to start and drove it home. It ran fine. Than it was right back to the sputter. I can hear the fuel pump run but it doesn't shutoff. Bad fuel pump? Any ideas on how to be sure before I drop $400 on this?