Could you guys help ? I am a pre 83 E21 320i J-K Jetronic guy and I don't have alot of inherent knowledge diagnosing engine problems with "Da Volavos ja !"

My symptoms are:
1) 19-20 MPG on hiway (really shitty gas mileage)
2) Have to feather the throttle until car warms up. (cold weather - below about 40)
3) Engine surges sporadically sometimes 50-150 RPMs.
4) Engine runs smooth then seems to "bog" down for a millisecond or two while cruising to work.
5) Sometimes dile drops from around 900 (when it decides to idle normally) to about 400 RPMs (in normal-warm engine conditon), I have to feather the throttle to keep the car from stalling.

What has been done so far....
The in tank sender unit was replaced last week
The "main fuel pump" still is a little bit "noisy" (IMHO)

My Guesses (but I need expert help, I hate easter egg hunting for problem)

1)Fuel Press Reg ?
2)Very oddly located vacuum leak ?( I have canvased the engine bay for vaccuum leaks didn't find any !)

Any help from brick specialists would be greatly appreciated !!

Regards,
Rich