I found the problem on my 1998 w140 s600,it has a intermittant crank sensor on drivers side,that ocassionaly will shut that part of the engine off for a second or two...my highly skilled mechanic,adviced me to try to tackle the issue myself,otherwise,the straight forward job is to remove the intake and fuel rail to get to them sensors(s600 has 2).Is there any way to get to them from underneath the car without taking the whole engine apart...this is a newer generation M120 that has sensors that can get unplugged,not part of the harness,so,that should help a bit...