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Discussion Starter #1
Does humidity affect a sensor or other part/regulator on the OM617? I have been running the last few (dry) weeks without even a slight shake from the engine. Today, after a few days rest for the ol' flapjacks, I've got a reasonably shaky idle. It is 71% humidity, and the barometric pressure is 30.03 inches. Is there something to check or clean that might create a shake when the humidity or pressure is high? I can't say it shakes more in the rain, but the barometric pressure is also low when it's raining.
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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The rack damper bolt/pin shows itself once the engine has warmed up, do a search, see if you can find a solution.
 

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Discussion Starter #5
Well, without any adjustment to anything, the shakes went away today. It was raining with 29.70 inches barometric pressure. Would this have something to do with the ALDA?
 

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I believe any influence the ALDA has would not be of the shaking variety, more of a smooth fuel restriction.

Humidity won't "tell" it anything, but pressure will.
 

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The ALDA itself, the pressure line from the manifold goes to the over boost protection device, then to the ALDA. This provides turbo pressure to the aneroid capsules.
If there is less atmospheric pressure, as in high altitudes, it will restrict the fuel flow.
 

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Discussion Starter #9
Thanks for that illustration. I will have to spend some time with it next week and see what I can determine.

Today was cloudy with similar barometric pressure to yesterday, and there were no shakes. It would seem that barometric pressure is having an influence.
 

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I have been reading the various Mercedes forums for 3 years and have not read this problem before.

I would check to see that my idle speed is within the normal range. (it is on the emission sticker on the crossmember in front of the Radiator on the Druvers side.)

Readjusting the Rack Damper Pin could not hurt either.

You also might clean out your Crankcase Ventilation Tubing. I found out if I put my Thumb over the Crankcase Vent Tube within 7 seconds the Engine started to try to shut itself off.
The reason given by another member is if the Crankcase Pressure is high enough it begins to push on the Diaphragm in the Vacuum Shutoff pushing it in the direction of shutoff.

A rough idle after the Engine is hot could be a symptom of a need for a Valve Adjustment.
 

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I had a similar issue with the 300SD. Keeping the tank full and adding Motocraft Cetane booster took care of it. All else was within spec - valves, ALDA, air and fuel filters...
 

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I noticed that my 300D performs and behaves better half way up the volcano (2000-2800 feet above sea level) than where I live at the bottom at sea level. This difference in elevation happens within 10 miles.
 

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Discussion Starter #13
Thanks for the input everybody. Everything is in spec, the valves are maybe in need of a slight adjustment, but it runs perfect at times, like glass as they say. Other times it feels like the car is sitting on a "magic fingers" bed. I've adjusted the rack dampener bolt twice to the point where it's just perfect on those good days.

Today is a high pressure day, but I might not get the chance to drive the car to further expand my theory.
 

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Normal atmospheric pressure differences at sea level are not enough to shake the engine or not. At high pressure the compression increases slightly, but at idle there is always enough air. The ALDA or similar altitude correction device restricts the fuel delivery at partial and full load, never at idle.
 

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Ah man...I don't wanna talk about shaky idles....mine is an undiagnosed mystery for 2 years now....
 

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Discussion Starter #16
It is 30.37in today with moderate shakes. Humidity is 92%.

It probably feels smoother today since I spent the last three days driving an M35A2.
 

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It probably feels smoother today since I spent the last three days driving an M35A2.
Bob'd or stock? :D

For what it's worth, my car shakes. Sometimes. I've tuned the adjustment bolt several times. It sometimes goes weeks without shakes. When I first got the car, it shook at every stop. Now I find it will shake more if I come to a faster stop vs just putting along and almost coming to a slow stop. I've thought perhaps humidity / pressure / vacuum hoses expanding/shrinking due to temperature, I've thought it's idle was too low, I thought it could be the linkage is dragging and needs more lubrication... All of it I have tinkered with and can always solve it that day I tinker... and then it comes back and goes away again...

The next thing I'm going to do is injectors. This will directly make the car run better due to a clear spray pattern. I'm also going to check the timing belt for stretch. I think all of these things can affect it, and it's a mix of everything to get them all perfect, for every day no shakes.

Dave aka Ghan
 

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Discussion Starter #18
Bob'd or stock? :D

For what it's worth, my car shakes. Sometimes. I've tuned the adjustment bolt several times. It sometimes goes weeks without shakes. When I first got the car, it shook at every stop. Now I find it will shake more if I come to a faster stop vs just putting along and almost coming to a slow stop. I've thought perhaps humidity / pressure / vacuum hoses expanding/shrinking due to temperature, I've thought it's idle was too low, I thought it could be the linkage is dragging and needs more lubrication... All of it I have tinkered with and can always solve it that day I tinker... and then it comes back and goes away again...

The next thing I'm going to do is injectors. This will directly make the car run better due to a clear spray pattern. I'm also going to check the timing belt for stretch. I think all of these things can affect it, and it's a mix of everything to get them all perfect, for every day no shakes.

Dave aka Ghan
It's stock and will stay that way other than maybe super singles somewhere along the line if I decide to keep it. I did have a use for it, but now I'm not sure what to do with it. :rolleyes:

Thanks for the input. I do the same thing, and I have it now where it runs great 80% of the time, so I guess that's about as good as it gets. :D
 

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Thanks for that illustration. I will have to spend some time with it next week and see what I can determine.

Today was cloudy with similar barometric pressure to yesterday, and there were no shakes. It would seem that barometric pressure is having an influence.

Funny, my sedan has same symptoms. Have you found any clues?
 

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Discussion Starter #20
I can pretty much tell once the car heats up if the barometric pressure is above or below 30.25" or so. Above it shakes, below it's like glass. But so far I am not sure what the cause is. I haven't had time to investigate further.

I believe that somewhere in the car something is adversely affected by barometric pressure that leads to intermittent shakes that seem to come and go day by day.
 
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