I am in the same boat on a 91 560, I believe mine is the air mass flow, my stall goes away with the eha disconnected but it is still hesitates and is rough when cold and a beast to start. But when warm it is almost perfect although still perceptable on acceleration.
I replaced the temp sensor although I knew it was un-necessary it only effects the start up and the manual provides a great test that is 100%. There is also an easy test for the throttle switch.
Make sure your duty cycle and EHA are in sync it is an easy test, and will help the narrow down the system issue.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)