Originally Posted by berfinroy

Assuming the gas in your Mercedes is unleaded and not THAT old (you said a matter of months, not years, get a hand or electric fuel pump and transfer it to a new car. Just be careful that the pickup fuel line isn't at the lowest point in your Mercedes tank where it might pick up some debris.
These first generation Bosch "D-Jetronic" are tricky. They will run, sort of, when one or more of the parameters are out of whack, but they will NEVER run WELL unless they are all spot on. they are:
1) Fuel pressure. You're already on to that. When the pump and filters are all clean and working right, the "Fuel Pressure Regulator" must be set to 30+/_ psi.
2) Fuel injectors. Bosch's injectors are very well designed and made. At minimum they should be professionally cleaned and matched for flow and spray pattern if not already done sometime in the last couple of decades.
3) Vacuum/fuel leaks. Lots of little hoses. Renew unless you know from inspection they hve been renewed in the last 15 years or so. INCLUDING the little short pieces that go from the fuel rails to the individual injectors. Gas leaks @ 30psi are dangerous.
4) Auxiliary Air Valve (AAV). Part of the warm up mechanism. The valve is supposed to close off supplementary air supply as the engine warms. They gat sticky with age and don't close properly, causing the idle to "hunt" in neutral. Look for a tutorial on this site for how to disassemble and renew it. Not hard, but not intuitive, either. Require so judiciously applied force.
5) Trigger points. Unique to the D-Jet system. They are located in the lower half of your distributor. Distributor removal necessary to inspect, clean and lubricate. They last a long time but maybe not 50 years! They carry very little voltage, so the actual points (4 sets) are probably OK, but the fiber blocks that ride the cams may be excessively worn if they haven't been lubricated, like, forever. The shoulder should be not much less than 1/8".
Bosch makes a repair kit, but its expensive.
These points are also subject to oil contamination rising up the no longer new distributor shaft. Other than just cleaning the trigger points for now, I suggest fitting an absorbent disc of some sort below the trigger points to block oil from getting to the trigger points. See other posts on "oily trigger points".
6)Throttle Position Sensor (TPS). On the right side of throttle body. Tells the ECU how long to open the injectors. The adjustment of this little gem is very touchy. If you don't have any symptoms of hesitation, crappy idle (assuming the other parameters have all been delt with) or a noticeable "on-off" fuel delivery sensation when you lift and apply throttle at modest speeds), leave it alone.
7) Plug wires must be sold core and plus non resistor type.
8) Compression. Valve lash. Valve guide seals (smoke on deceleration) Valve timing---this engine has a long chain that gets excessively stretched in time.
Now go have fun!