90 560SEL M117 Won't start after rebuild

I just finished installing the engine and found a new problem that didn't exist before I started the project. The engine will not start unless I "prime" it with a little gas poured into the intake. It will
immediately stall unless I feather the throttle and keep the RPMs above 2500. Even then it seems like it once to stall but that might be timing. I can't keep it running to adjust the timing any further but I don't think that is the issue with starting. Before I tried starting the engine I installed a new fuel filter, flushed the lines and tested the flow rate, the pumps seem OK. The idle valve is clean (along with the rest of the parts).
Any ideas on what to try? Is there a way to test the pump fuel pressure at the fuel distributor? If so how do I connect my gauge and what should it read when I engage the fuel pump relay? Can a fouled up idle controller cause this much trouble? I've had them go bad before but never had this type of problem.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Timing would have to be way off to cause such a problem and the fact that it runs after being "primed" confirms the fuel pump is operating.
I suspect a large vacuum leak which would account for the 2,500 rpm minimum speed, the need to "feather" the throttle (to reduce air vs. fuel) and the need to "prime" the motor to get it going. (By the way, "priming" is VERY dangerous to do.)
I suggest you go over the main vacuum connections to the intake manifold to ensure they are connected and correct.
--

2008 T.G.Lambach. Publication in any form requires prior written
permission.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.