I had a similar problem with my 740 GLE wagon ('87) this fall--out teaching my daughter to drive, and it started doing this out of the blue as we were switching drivers. I limped it home--it'd run fine, if I kept my foot in it, but died at stop signs, so I'd rev it up, let off the brake, and drive like heck to the next sign : ) --anyway, got it here, mechanic hubby popped the hood, and a vacuum line (sorry, I don't remember the exact name; it was a thick one, about the size of my thumb) from the top of the air "snorkel" to the block had popped off. He put it back on and it's been fine ever since. This hose didn't have any kind of clamp/pinch-type factory clamps, etc. on it--it just went onto the tube extending from the engine on the driver's side, about halfway back--very visible. If more info is needed, let me know; I can ask when he gets home from work and forward more precise terms to help. (Sorry, I know a lot of what goes where and how it works under the hood, I just don't always remember the technical names--it's usually "that black thing that hooks onto the metal flange" sort of thing with me! : )

Good luck!