Same exact problem my '97 E420. Had from when it was new. Back when it was new the dealer tried and tried to fix - and finally could not so what they did was move the idle up somewhat so that it idles faster. That basically corrected in that the surges are less noticable and on the downstroke it no longer hiccups like it wants to stall. Only problem is that with the faster idle I have to press harder on the break to keep the car stopped. Therefore I drive in the "w" mode, rather than "s", which means the car starts in 2nd gear instead of 1st. Actually this is not so bad, as the E420 has so much power, it is fairly jerky starting in first gear, and I sort of like starting in 2nd (same as my old '87 420 sel did). Sorry this doesn't help you - but now you know you can reprogram to boost the idle and it will be much improved if you can live with that.