That's either a leaking Fuel Pressure Regulator or an leaking injector.
Pull the vacuum line that leads to the FPR and smell/feel for the presence of Gas. If there's any, replace it.
To check the injectors, hook up a fuel pressure gauge, block off the return line and vacuum line of the FPR, turn the Key on/engine off and read the pressure of your system. If the pressure doesn't hold steady, one/more of your injectors are leaking.
You could replace one injector at a time. But if there's more than one leaking, I suggest you replace them all. If you don't, you'll have driveability issues, as it's hard for new injectors to balance correctly with old injectors. And your computer can't always compensate for the imbalance.