I have a 1983 300SD (126 Chassis). The car has a serious vibration when in idle and and low speeds, the vibration is somewhat less at higher speeds but is still noticeable, also the engine does not shut off when the key is turned off and removed from the vehicle!! I have to choke it with a hard step on the accelerator and turn it off immediately at a high RPM. I believe that this is a vacuum leak (I may be wrong of course); if in fact this is symptomatic of a vacuum leak could someone with the expertise please point me to the right vacuum hose or hoses which should be checked. If I am wrong please give me your best suggestions on how to find the source of this problem and what steps to taken in order to fix it. Thank you. Haresh