residual pressure valve???

[der affe]

does my 91 325i have an RPV for the fuel system? is it just part of the fuel fress reg at the fuel log? the car is acting like the fuel press is bleeding off if it sits for a legnth of time. once it seems to build up pressure it runs fine (although i put a new press reg on it this morn that i had laying around). my mpg has been getting worse over time recently, and with the new press reg it seemed to have better power (it was smoking upon accel. before) and get better mgp today. it still took many attempts at cranking to get it to light off though, yet if i turn it off after running it it fires right up???????? any ideas????
thanks,
greg

[PiercedE30]

its in the line next to the fuel pump under the back seat.

[der affe]

thanks!