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Discussion Starter #1
Hi folks. I replaced plugs wires and coil’s in my M104 motor. I had a little hiccup on idle … Just a little blip where the oil pressure would bump up a little bit and I could feel the car shake. VERY mild but noticeable....After replacing everything I still have the same issue. Any ideas?

Plugs: Bosch F8DC4
Wires: Beru
Coils: Bosch
O2 sensor: Bosch
 

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That sounds like a coil symptom.
 

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Let's address the elephant in the room. . . . eco junk wiring. If the harness and throttle body have not been replaced (rewired does not count), then all bets are off.
 

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Discussion Starter #6
When were the motor mounts and transmission mounts last changed?

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Haven’t changed yet. Just rear flex disc. I have a trans mount but after I removed the cross member to replace I could not get a socket or wrench on the bolts because of a flipped up metal tab on the existing mount.
 

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Discussion Starter #7
Let's address the elephant in the room. . . . eco junk wiring. If the harness and throttle body have not been replaced (rewired does not count), then all bets are off.
Thanks. The upper harness has a build date of 1/03, Delphi . Lower harness not rebuilt yet but does show signs of breakage and greenish wires can be viewed in spots. Throttle body harness could be a factory replacement perhaps? When I opened up the harness loom to inspect, all of the wires looked to be made of black insulation and there was no corrosion on any of the insulation at all.

Idle seems to be around 650 ( Buy dead reckoning )
Coldstart idol is above 1000 then drops to normal idol within a minute.
Smog pump runs for a couple minutes then shuts off. Seems normal I guess from what I’ve read.
Mileage is about 19 mpg all around.
2602692
89369106-77D2-4B93-A988-79E71F472965.jpeg
2602693
3741F837-D3B4-4992-96B0-918626E6EA69.jpeg

The first pic shows the condition of the throttlebody loom. The second pic shows the lower wiring harness condition
 

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Discussion Starter #9
Here’s a photo of the loom before I dissected to inspect. The arrow shows where I cut. Should I see evidence of rebuild at the connector? I’ve seen how they cut around the connector in order to separate it to replace wires and then “glue” it back together (which looks terrible) . Or should I disconnect the connector to see what the condition of the pins are? I don’t know how else to look for evidence of a rebuild. The harness sheathing seems to be the same thickness as factory.

Side note. I have a spare TB from an e320....down side is I don’t know mileage of that car. That loom has obvious “green” decayed wires...don’t know if paying for a proper rebuild on that would be worth it.

2602726
 

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Check the green label on the throttle body. Look for the date code in the corner. Should look something like xxMxx

Anything prior to 1998 is eco junk in my book, regardless if the unit has already been rewired or not.
 

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Discussion Starter #11
These are both of my throttlebody date codes. The one on the car the dot matrix is scrubbed off. So the best option is to get the post 1998 used ?
2602736

2602737
 

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Discussion Starter #12
The second picture looks to read 95M10.... looks like I should’ve just left it there on the car. I’m aware of the two rebuilding services , (Victor and another service on eBay ). but if my best bet is to look for a post 1998 used… Perhaps with low miles then I could go that route.

Getting back to the main problem it’s not that bad necessarily. But this being my first ever Mercedes I don’t have a baseline of how this 2.8 L motor should run. I think overall it’s running fairly decent. At WOT On the expressway, acceleration seems a little flat. But again I have nothing to base this on.
 

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If in doubt, throw it out. These cars are impossible to troubleshoot if the eco junk bug is still at play.

And yes, using 1998 and up components is the sole way to ensure you have eradicated the eco junk disease.

A properly running M104, especially one with HFM, should be completely vibration free and very smooth all the way to redline.

Here is a EZ 20 second quick test I use. With the engine running, put a glass of water on top of the engine between the oil cap and the the air crossover tube. Stick a coaster or something containing standard 12pt size text underneath the glass. If you can still read the text with ease looking up from above, you can pretty much rule out ignition components. Move the glass along the length of the engine and repeat a couple more times.
 
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Beezersh
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