Rough-running W124
 

My 1993 300E2.8 has been as solid as a rock the past few years, but the past few days it's been behaving oddly.

Yesterday while I was waiting for a friend in a parking lot it sounded like it misfired briefly, but continued running as normal.

The next time I started it up, it was really running roughly with really strong vibrations, as if it was about to stall out on me.

I got the car home, noticing that the vibrations seemed to go away once the car was above 35mph. I started the car up again this morning and the vibration was still there.

Any ideas, anyone?

yes
 

where I would start here is to make sure all the spark plug lines are secure....they can come loose....it's free as well...

if
 

even 1 cylinder is slightly misfiring the entire engine will feel not right.

i would check all plug wire connector ends and check the distributor rotor.also check fuel pressure with a gauge.

I'll go out and check the spark plugs and wires tomorrow - it's pouring with rain here, maybe some water got in somehow. I do have a second set of spark plugs (but not wires) I can replace these with if need be.

If I know one thing, M104s don't have a distributor cap/rotor assembly, their ignition is electronic.

Make sure you have the correct specified plugs, Any deviation to plugs like platinum or multi anode variety do not mix well with M.B's

oh my bad, if its electronic ignition,there is a strong possibility,of one of the coils having a crack on the bottom or top allowing moisture to enter it,or it could be internally shorting out,remove the coil pack,inspect all the ends around the hard urethane sealing. look for dark or brownish discoloured spots,also smell the coil,if you smell any burnt electrical smell its possible you got a bad coil pack,this will almost always cause a misfire intermitently.sometimes the cylinder loads up with fuel,then it misfires causing a bang or a ruff running feeling.also check the electrical post ends for corrosion,sand them all down lightly then apply dome dielectric silicone to them and reapply the silicone wire boots.

I learned the hard way after replacing all the parts and some very expensive at that. On this engine, always replace the oxygen sensor even though the lite is not lit on the dash. That will probably take care of the problem.

Steven, my guess is that one of the 3 coil packs is shot, probably the rear one. To avoid throwing parts at the problem it's best to try a known good coil in each of the three locations to see if it resolves the misfire. If one of the coil packs is bad the engine will also lack power. I have had a coil pack fail instantaneously ... one minute it's fine, upon restart the engine is misfiring and shaking.

It's a good idea to replace the coil boots/connectors also.

Check the codes.

Most likely is a plug/wire/connector/coil.

For all those of you watching the thread like a hawk (which was probably just me anyways) I finally got around to diagnosing the problem.

It turned out that it was the plug boots and/or wires. I installed a new set this afternoon, and the vibrations are gone.

I'm suspecting it was cylinder number 6, the boot covering the plug had a lot more oil on it than I expected it to and I wonder if that oil may have caused a problem in the electronic ignition system.

If the wires are bad i would bet those coils are OLLDDDD! and shot. Because if someone wont replace 150 dollars wires the coils never got a second look. Id bet the cap and rotor are pretty bad also at 60 dollars or more for the set.

Scroll up a bit - this car doesn't have cap and rotor :)

But yes, coils are on my shopping list. They're a bit more expensive than the wires, so I wanted to replace them first to eliminate them. I've owned this car for about 10 years and I don't remember replacing them, it's almost certainly time for a new set.

If it has the light blue top coils still then I would seriuosly think about replacing them. One of mine went out at 140 000km in my 104.

I believe later variants were just black.

Woo, resurrecting my own old thread - I've been driving my other car until I can get around to fixing this.

I did pick up a set of wires, replacing them didn't fix the problem. My next thought is spark plugs, it's time for a new set anyways.

The coil packs I have are black, so it sounds like I have the older style, but if the new spark plugs don't fix it, then I'll move onto those.

I did notice that there's a very faint smell of fuel when I start the car up, either warm or cold. Could a bad injector cause this problem too?