Engine/Transmission (1998.5 - 2002) fuel leak and bad mileage?

[SamBrown]

hey guys, my buddies 99 24v has a small fuel leak coming from the nut on the injector line at the cylinder head. he has been complaining about poor mileage, around 10-12mpg. his engine also idles slightly rough. it is all stock and i already cleaned the iat and map sensors. could this leak cause this condition? the help is appreciated guys

thanks

 

[bmoeller]

Is the nut tight?