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1992 Mercedes Benz W124 230E, 200k mi
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Discussion Starter · #1 ·
Hi,
I have been trying to figure out my 230E´s (1992 200k miles M102.985 engine) running problem for pretty much 15 months now. It started with some occasional vicious misfires that seemed like the whole engine cut off for a tiny moment before running normally again. I changed all plugs, whole distributor and distributor cap, ignition coil and all wires between the coil and the plugs. This did not have much effect (though I do think it ran quite well for a moment after the coil change but that could be purely a coincidence) and the running continually got worse and soon it also started to stall on idle.

I managed to get the car to my trusted repair shop where it spent a few months. During the time they found a leak in the intake manifold gasket. That was fixed which apparently cured the misfire. However the idle problem remained unsolved. The car also had quite a bit of oil in the breather hoses and air filter, probably caused by the faulty gasket. As I drove the car back from the repair shop after about 15 minutes the misfires came back.

I subsequently did a smoke test by attaching a home made smoke machine to the brake booster vacuum line and found a leak in the rubber bottom of the fuel distributor which I then changed (and cleaned the whole fuel distributor). I also at some point got the car to maintain idle by fiddling with the screw on top of the distributor. However the idle was rough and very high alternating between 1000 and 2500 rpm. Although the idle was horrible I did a short test drive and on driving rpms the car first ran very well. However after about 10 minutes the misfires came back.

Lately I have been trying to troubleshoot the problems by going through earlier posts in the forum and changing parts that have been suggested to be at fault in similar cases. I have recently changed:
OVP relay (new)
ECU (used)
Fuel injectors and their rubber holders (new)
Battery (Used)
Idle Control Valve (cleaned and tested the old with 9V battery and found it opened and closed properly)
Some breather hoses that seemed brittle

I also did a compression test and all the cylinders were quite evenly at 180psi. I also flushed the coolant which was clear and so I suspected I likely do not have a blown head gasket. I did redo the smoke test as well and found no leaks.

Right now the situation is that when I start the engine it idles very high (about 1300rpm) and the whole car unevenly shakes while idling. If I give it some revs the idle sticks to close to 2000rpm. Besides the shaking the engine does not really misfire or cut off. However if I go for a drive, after a short while as the engine warms up, the violent misfires return.

I am not an experienced mechanic and just trying to save the little money I have by trying to fix everything myself (especially as all the people from repair shops have been just as lost as I have and I don´t want to pay thousands for diagnostics). However right now I am quite lost and don´t know what to try next. Does someone have any suggestions? I am open for any ideas.
 

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W124
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5,837 Posts
It sounds like you adjusted the fuel mixture screw and now you have an idle issue. I would put that screw back to where it was and find the real cause. Unfortunately I don't have any experience with the 4 cylinder motors because we never had them here. Possibly someone from another marketplace will step in and offer some suggestions.

lf your distributor has an orange plastic disc behind the rotor mount, replace it. These are going bad now after 25 years on all of the engines Mercedes used them on. My guess is that you have a fuel enrichment issue but I am not familiar with which devices are on your engine.
 

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W124, 230E 5 speeds Manual, 1987
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295 Posts
How did that problem start? Suddenly? or after some works on the engine. is it the same when cold and Warm?
If the shop you're taking your car to is familiar with those engines he should have checked those basic things:
Duty Cycle measurement
Your engine timing?
Fuel pressure test and identifying the fuel pressure regulator and fuel distributor conditions? you never mentioned any fuel filter replacement or Microfilter replacement (the one that is directly attached to the Fuel distributor inlet)
Cold start injector if it is stuck open and leaking?
Oxygen sensor?
EZL Ignition control module and ignition coil? if the problem seems to be in the ignition side.
 

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1989 W124 260E
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3,125 Posts
Replace fuel injectors ..Fuel is entering the engine at the wrong time through worn injectors, or cold start injector, they in turn leak fuel in to the exahust manifold and then it ignites inside = backfire .
 

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W124, 230E 5 speeds Manual, 1987
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295 Posts
Replace fuel injectors ..Fuel is entering the engine at the wrong time through worn injectors, or cold start injector, they in turn leak fuel in to the exahust manifold and then it ignites inside = backfire .
According to the op first post he has already replaced the injector. A bunch of another issues can cause a backfire or an intake fire other than worn injectors.
 
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