I had this same issue when i purchased my 400 E nearly 3 years ago. The car had 64,ooo miles on it and after alot of frustration i used the the cable atached to the accelerator to up the rpm about 150 ...once over 500 rpm's no more issue...adjusted the shift linkage to move it back to the same relationship and have NEVER had the car stall again. I've been pondering the idle bleed screew throat is clogged just enough to keep it from functioning correctly but haven't taken the time to mess with it...lincoln town cars or more specifically the 4.6 liter engine used to have the same problem and the dealership said the clogged idle bleed screw passageway was the problem...and it was...I had one. Good luck. I'll be curious if the tweek is more effective than tightening the cable enough to open the butterfly a split hairs worth.

Brian