hello, i need ur help guys/gals........

i have a C240 auto, lately it has developed the ff. problem with 8,000kms++mileage:

a) Car starts fine, runs fine also, no problem with acceleration.
b) Engine idles at 700+sumthin on idling with aircon-OFF
c) Engine rpm "sometimes" drops to 500+ engine shakes for a few seconds before recovering to 700rpm when aircon is turned ON. sometimes, d engine dies! this happens when d engine is cold or hot


d) When i start d car, with Aircon ON or OFF, and shift to "reverse" or "drive" and with my foot on the brake pedal, and without stepping on d throttle (simulating traffic stop with gear in D), engine rpm goes down to 500rpm range, then engine dies! in short, i cannot anymore hold d car by depressing d brakes with the selector in either D or R, d car will die after a few seconds(randomly-but most of d time), to be able to use it, i have to shift, then throttle immediately to prevent d engine from dying. or while in traffic, i have to shift either to N of P for d engine to hve d correct idling rpm, otherwise..engine rpm goes down to 500 and dies.

however, when i pass over some speed bumps--or slowing down at an intersection or traffic, sometimes, d engine just dies!!!

what could b the problem for this????????????/ its really bothering me alot coz i dont hve a benz dealer in my place! and it seems...im gonna b spending to import a mechanic to my city, and thats gonna b bloody for my wallet