BMW Repair: 86 325es surging all the time, fuel pressure regulator, air flow meter

Question
My 325 es engine  surges all the time at any rpm. It isnt one rmp it happens at mostly all. Question..  what is the part that looks like a pressure regulator just after the fuel pump and what is its part number? mine is real rusty and needs to be replaces  bet.

thank you Charles.

Answer
Charles,
 These cars are notorious for this problem, and I've fixed my own and several other people's cars.  However it was usually a different reason for the surge on each vehicle!

 Things to check:

 - Air Flow Meter
 - Idle Control Valve
 - Fuel pressure regulator
 - O2 sensor
 - Temp sensor on thermostat housing
 - All ignition components

 The thing that looks like a fuel pressure regulator, but is mounted by the external fuel pump is a fuel surge dampener.  It is just a diaphram with a spring behind it.  If there is a surge of high fuel pressure, this diaphram will deform and absorb the excess pressure, instead of busting a fuel line or something else.  Some cars didn't have them from the factory, so it's not a necessary item.  So do what you feel comfortable with.

 Hope this helps,
 Josh