Two possible pieces they could have indicated. The fuel pressure REGULATOR is a mechanical device that maintains fuel pressure by dumping everything but the set pressure back into the tank. (This is dependent on the fuel pump providing enough volume that it can be regulated).. This device causes mixture problems by varying the pressure. It usually fails in the closed position and this about doubles the fuel pressure, making it go rich.
The other device, more commonly the problem doens't have to do with fuel pressure but is called the intake manifold pressure sensor. This device shows the manifold vacuum level to the control unit which uses it to determine relative engine load. It makes up about 60% (or more) of the fuel calculation and can really screw with the running.
Both devices require somewhat special tooling and experience to evaluate. Get your records of their recommendations and be sure which part they diagnosed as you appear to have already paid for a diagnosis.
Bosch Master, ASE Master, L1
33 years MB technician