Have a helper press the accelerator pedal to the floor and make sure the rack lever on the back side of the IP is actually moving to the full fuel stop. It's certainly possible that something is wrong and preventing movement of the rack lever.

Also, even though it may sound stupid.....have you checked for a mouse nest or a rag or something caught in the intake or airbox? It happens...

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]