Engine misfire

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S 500 - 1995 ( V 8 ) with 40.000 Km, only dealer MB inspections, like a brand new. Randomly looks like one cilinder misfiring. The RPM in idle goes up and down about 100rpm and I can fell a minor shaking engine, sometimes cold, sometimes warm ,sometime hot and sometimes a weeks long nothing happen. (flawless) At MB computer dealer don´t show any wrong codes. Anybody can help me with sugestions what the next step?
Thanks in advance.
Malachias (Brasil) :screwy:

That's odd, if there was a misfire problem the computer should have logged it. My guess is not a misfire problem. I have rarely seen a 119 engine that did not have a loose, broke, or decayed vacum line somewhere. Pull the air box and look around the intake paying close attention to the vacum lines on the intake. Look at the large vacum line that runs from the EA actuator(throttle body) to the right side valve cover...that line is prone to decay. You will have to grab hold of it and pull, twist, and touch every part of it, if it doesn't come apart in your hand then it's probably o.k. Also, there is a small group of vacum lines on top of the intake that rum from the left front of the engine across to various points, those are small plastic lines about the diameter of a pencil and they get very brittle. Check ALL the vacum lines, large and small.

That's odd, if there was a misfire problem the computer should have logged it. My guess is not a misfire problem. I have rarely seen a 119 engine that did not have a loose, broke, or decayed vacum line somewhere. Pull the air box and look around the intake paying close attention to the vacum lines on the intake. Look at the large vacum line that runs from the EA actuator(throttle body) to the right side valve cover...that line is prone to decay. You will have to grab hold of it and pull, twist, and touch every part of it, if it doesn't come apart in your hand then it's probably o.k. Also, there is a small group of vacum lines on top of the intake that rum from the left front of the engine across to various points, those are small plastic lines about the diameter of a pencil and they get very brittle. Check ALL the vacum lines, large and small.
:smokin:
Thanks Talonlover for your replay. You are sure about no logged MB comp. because misfiring is a ease problem for to fix, even in Mercedes S class and the computer should grab any code. Every time that I did the PC test hunting for a code, as I said. this happen randomly ,the engine was flawless
I checked my vacum lines. It`s OK. I will let you know when I found what is going wrong.
Thanks again.
Malachias (Brasil)

:bigthumb: :bigthumb: :smokin:
Thanks Talonlover for your replay. You are sure about no logged MB comp. because misfiring is a ease problem for to fix, even in Mercedes S class and the computer should grab any code. Every time that I did the PC test hunting for a code, as I said. this happen randomly ,the engine was flawless
I checked my vacum lines. It`s OK. I will let you know when I found what is going wrong.
Thanks again.
Malachias (Brasil)
:grinyes:
Dear Talonlover:
I came back over my vacuuns hoses again, now with more accurate looking, as you advise me, and finally I found a small S form hose that goes in the fuel pressure valve was decayed. This was possible when I stop the engine in one silencer spot and I could hear a a very low ZZZZZ ( sound) coming from the port from the engine ( negative pressure). I fixed this hose and put a period in my long time headake.
My thanks again for your help and knowledge.

Malachias (Brasil)

Very glad to hear you got the problem fixed!