Hello! I just bought this 1995 Mercedes S500. The car has less than 140k miles. It is in nearly excellent shape inside and out and looks as if no one has ever sat in it! While driving home today, the car acts as if it is going to stall and wont downshift when you floor it, making it very hard to get up hills. I pulled into a gas station and got gas. Trying to pull out of the gas station the car kept stalling. I eventually got going and drove about a mile down the road and started to smell like an electrical rubbery burning smell. I shut the car off and rolled into a Walmart parking lot. There was a ton of smoke coming out of my rear vents ONLY and under the hood from behind the engine and above the transmission. It smoked for about 3 hours (not kidding) with the battery disconnected until the tow truck arrived. The center console wood and the metal part on the shifter were VERY hot. That was last night. The car still starts and runs when cold but not very well. only started it to move it a little in the driveway from where they dropped it of and disconnected the battery again. So far today I've cut a bunch of slits in all the rubber wire coverings to find nice shiny wires inside. All brand new. I did lift it up last night with the spare tire jack and put some bricks under the side so I could crawl under and see what was smoking. I couldn't see anything. I have no idea what to do. It didn't smoke before but it did run awful and the guy I bought it from had it diagnosed as a crank position sensor.. please help! No idea what this could be. The wires I think look OK in the center console but I only removed the button wood around the shifter. There seemed to be more smoke coming from the spot under the hood even after the vent smoke in the rear stopped.

 

So I looked under the car a little closer now that's it's light out and found this! I looks as if the exhaust got too hot and caught the insulation on fire that's around it. I cut the harnesses open that were under the car to find Shiny wires still. I'm thinking it may be the crank position sensor? Responses are appreciated!

 

Was the wiring harness replaced? If you still have the original harness they are known to fail on all pre-96 W140's. Remember there are 2 harnesses...

 

Yes the throttle body harness amd the one for the injectors and everything on the top was replaced. I've cut open every wire bundle I could see and only found nice new wires. The exhaust got hot and melted the insulation around it under the car.
The car runs rough on startup cold and gets worse to the point that it barely runs at all when it's warm. It is extremely difficult to accelerate and smells like rotten eggs from the exhaust. Too much fuel and not enough spark.no check engine light either.

 

What fixed your problem?