I am totally new to Mercedes-Benz's. But, I just bought an 88 560SEL. . .very, very clean inside/out. . .with 99k on it for $5200. A/c great, all electrical stuff works, never been wrecked, etc. The car will start and idle usually just fine. . .no weird noises or anything else out of the ordinary. However, under acceleration, it will fall flat on its face and stall. I can get maybe up to 30mph before it "misses". It will stall. I put it in neutral and it will start up just fine. . .then the same thing happens again. If this was a car that I was familiar with, I would say either clogged fuel filter and/or bad fuel pump as I have run into this with other cars I've owned. I got a CarFax report on it and the report says that at times over the last 17 years it just sat. . .the use of the vehicle by the prior owner did not seem to be ordinary or daily. Could it sitting around have caused some rusting to occur in the tank, and the rust has clogged the fuel filter? Or, could it be something more complex? It is not the transmission because there are times when it will have a hard time starting after one of these stalling episodes. And, the missing/stalling seems to also occur at low speeds rounding turns. All opinions respected and appreciated.

First thing that I would do, is inspect all of your vacuum lines...make sure they aren't cracked/broken. Physically inspect them when you can reach them...bend them, tug on them, make sure they are still good.
Next thing (that would involve no $) would be to check the cap and rotor...clean the contacts if they look groady...(if you notice any improvement that could very well be your problem). After the cap and rotor check, inspect the ignition cables themselves...I've read that you can spray a mist of water on them at night, and observe arcing if they are in need of replacement.
After that, you can spend a few dollars on a fuel filter, and see if that lends any improvement.

OH! Check the timing...It just occured to me that the timing chain rails might be original...and the possibility that something is awry is there. Do a search on this subject (make sure you have a little time). If you should find out that the chain and rails have already been replaced, check the timing again to make sure it was re-assembled right. Is the "Economy" gauge (aka vacuum gauge) giving you any hints? ie: when it idles, where is the needle? when it is "stumbling" where is the needle?

Good luck in locating your troubles!

-Larry

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09 Jetta TDI
1985 300D

I had a similar issue with my '88 560SEL and it turned out to be the ignition coil.

I have an issue with my fuel injectors, however they cause the motor to idle rough at low RPM and smooth out at higher RPMs


Good luck!

I had a similar issue with my 560 SEL way back. It was one of the vacuum lines that was broken. It would stall and die but will restart. I changed the line and it fixed the problem

UPDATE: I now have the car at a supposedly reliable Mercedes-Jaguar-BMW garage here in Las Vegas. It came recommended to me from a friend of mine. So far, they replaced an O2 sensor that was supposedly bad. . .the Check Engine light had been on and they said replacing it would fix it. Also, they checked out the fuel distribution system and some other things under the hood. I asked them if they thought it was a fuel filter or fuel pump problem. They said no, saying that the filter had been checked and the fuel pumps had given regular voltage readings. So, they concentrated on the above mentioned things. Now, today. . .Wednesday. . .they tell me that the other things they fixed did not change the cars stalling/missing. They are now looking at the fuel pumps and telling me that the pumps appear to be "used". . .as if somebody else had replaced the originals with used parts, saying they look as if they had been "painted." Who knows. . .but has anyone ever heard of this? As a side note, on Monday night before I dropped off the car at the garage, I noticed that at the back of the car a very audible whirring noise that I had not heard before. How loud are fuel pumps on this car supposed to be? I'm beginning to think this is something really simple that these guys are missing. . .like a vacuum line or a corroded ground wire dealing with the pumps or something in the fuel system. Also, the car revs fine in neutral. . .only when it is pulling a load does it miss. What's the life for a fuel pump on this car? The car also has rotted motor mounts that need fixed. . .this car must have sat quite a bit.