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2002 ML320
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Discussion Starter #1
Hi everyone, I could use some advice on how to troubleshoot and fix an issue. I have a 2002 ML320 with 250K miles. This issue has been gong on for the last 30K miles. I know I should have addressed it early. While driving the engine seems to lobe a bit. What I mean is that between 2000-3000 RPM, mostly around 2300 RPM, the engine will lobe and I can hear and see via the tach that engine fluctuates about 25-50 RPM. When the vehicle is underload (going up a hill) the lobe seems to be more present during the 2000-3000 RPM. If I get out of the 2000-3000 range, the lobe seems to go away even while at constant throttle. Here is what I've done so far.

1. Replaced the coils and plugs 240K. Didn't resolve the issue
2. New air cleaner
3. Cleaned the MAF with proper cleaner
4. No engine codes

Any thoughts on how to troubleshoot? I do have an Autel Full System Scanner MD802 Maxidiag Elite and can't seem to determine the cause. Any help is appreciated.
 

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2002 ML320
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Discussion Starter #3
Hi Witek_M, thank you for the response. I'm wondering if a vacuum line could cause this issue. In the images below, there is a line that goes from the sensor shown to the underside of the bottom side of the intake manifold (towards the front). The line was falling apart. I did cap the end off the sensor. I also I tried to put a plug in the line on the bottom of the manifold (not sure if the plug was inserted completely because the line broke at the lip of the manifold). I'm not sure what that vacuum line controls. Could this be the issue? The vehicle does seem to lobe slightly at idle now that I think about it. I thought the issue at idle just might be due to the AC cycling. Also, how do I replace that line if you think this is the issue? It appears the line goes directly into the manifold and is nearly impossible to access without removing components.
2613801
2613802
2613804
 

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2002 ML320
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Discussion Starter #4
Hi Witek_M, thank you for the response. I'm wondering if a vacuum line could cause this issue. In the images below, there is a line that goes from the sensor shown to the underside of the bottom side of the intake manifold (towards the front). The line was falling apart. I did cap the end off the sensor. I also I tried to put a plug in the line on the bottom of the manifold (not sure if the plug was inserted completely because the line broke at the lip of the manifold). I'm not sure what that vacuum line controls. Could this be the issue? The vehicle does seem to lobe slightly at idle now that I think about it. I thought the issue at idle just might be due to the AC cycling. Also, how do I replace that line if you think this is the issue? It appears the line goes directly into the manifold and is nearly impossible to access without removing components.
View attachment 2613801 View attachment 2613802 View attachment 2613804
That is right in the middle of range when variable intake operates.

That is right in the middle of range when variable intake operates.

Seems like the vac
Hi Witek_M, thank you for the response. I'm wondering if a vacuum line could cause this issue. In the images below, there is a line that goes from the sensor shown to the underside of the bottom side of the intake manifold (towards the front). The line was falling apart. I did cap the end off the sensor. I also I tried to put a plug in the line on the bottom of the manifold (not sure if the plug was inserted completely because the line broke at the lip of the manifold). I'm not sure what that vacuum line controls. Could this be the issue? The vehicle does seem to lobe slightly at idle now that I think about it. I thought the issue at idle just might be due to the AC cycling. Also, how do I replace that line if you think this is the issue? It appears the line goes directly into the manifold and is nearly impossible to access without removing components.
View attachment 2613801 View attachment 2613802 View attachment 2613804
Hi Witek_M, thank you for the response. I'm wondering if a vacuum line could cause this issue. In the images below, there is a line that goes from the sensor shown to the underside of the bottom side of the intake manifold (towards the front). The line was falling apart. I did cap the end off the sensor. I also I tried to put a plug in the line on the bottom of the manifold (not sure if the plug was inserted completely because the line broke at the lip of the manifold). I'm not sure what that vacuum line controls. Could this be the issue? The vehicle does seem to lobe slightly at idle now that I think about it. I thought the issue at idle just might be due to the AC cycling. Also, how do I replace that line if you think this is the issue? It appears the line goes directly into the manifold and is nearly impossible to access without removing components.
View attachment 2613801 View attachment 2613802 View attachment 2613804

I just read this thread > https://www.benzworld.org/threads/intake-manifold-vaccuum-hose.1492201/#post-3906284. My hose was completely deteriorated and broke when I moved it. However, I had the lobe issue before I messed with the line. If this could be my issue, then this looks like a time consuming job.
 

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2002 ML320
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Discussion Starter #5
Seems like the vac




I just read this thread > https://www.benzworld.org/threads/intake-manifold-vaccuum-hose.1492201/#post-3906284. My hose was completely deteriorated and broke when I moved it. However, I had the lobe issue before I messed with the line. If this could be my issue, then this looks like a time consuming job.
Ok, you think its the vac line. From what I've read this is replaceable but requires the removal of the intake, correct? Does the male connection for the line reside inside the intake? In other words, does the line get inserted into the intake or is there a male protrusion outside of the intake that the line attaches?
 

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2000 ML55 sold😢 2013 ML500,😁 2015 C250 estate wagon, 1927 Dodge 4 sedan, 1929 Dodge
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What you can do with that line is get some plastic tube that fits inside your vacuum rubber line. Cut a piece about an 1” long and slide it into your broken piece that goes into the manifold and then slide the new vacuum line onto it. Use a tiny bit of loctite super glue on the very end of the rubber vacuum tube before you put it in. Then go about replacing all your vacuum lines on the whole engine.
 

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This is where the line goes to inside the plenum chamber.
 

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Ok, you think its the vac line. From what I've read this is replaceable but requires the removal of the intake, correct? Does the male connection for the line reside inside the intake? In other words, does the line get inserted into the intake or is there a male protrusion outside of the intake that the line attaches?
It is convoluted design with vacuum reservoir on the bottom of manifold.

Read this and all links within.
 

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2002 ML320
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Discussion Starter #9
What you can do with that line is get some plastic tube that fits inside your vacuum rubber line. Cut a piece about an 1” long and slide it into your broken piece that goes into the manifold and then slide the new vacuum line onto it. Use a tiny bit of loctite super glue on the very end of the rubber vacuum tube before you put it in. Then go about replacing all your vacuum lines on the whole engine.
Hi mattml430, that is an interesting idea. I'll try it this weekend and get back to you with the results. That area is really difficult to get into. However, I do have some angle pliers that might be able to get under the manifold and provide enough lift to push in the tube. My concern is that the vacuum line in the intake manifold might get push up while trying to insert the tube or I won't be able to insert the tube. Have you tried this or is this just a novel idea that you just came up with?
 

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It’s a novel idea that worked quite well for me. Lol
 

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2002 ML320
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Discussion Starter #11
It is convoluted design with vacuum reservoir on the bottom of manifold.

Read this and all links within.
Hi Witek_M, thank you for the link; which contained excellent information as well as photos. I now see the design of the ribbed vacuum line and see why it was impossible to remove. I guess we can all Monday morning quarterback that design, but it is what it is. It doesn't appear that the vacuum line is available for purchase. Moreover, it appears manifold would need to be split to replace and that then becomes an issue since there are no replacement gaskets. Therefore, it looks like I have three options.
  1. Attempt a repair as mattml430 suggested to see if that works without removing the manifold.
  2. Remove the manifold and attempt splicing a new vacuum line or metal vacuum line into the remaining piece of vacuum in the intake manifold and seal with RTV to ensure no air can get in from the outside.
  3. Replace the entire manifold with a new one. If option 1 doesn't work, I then think this would be the best choice.
Any additional thoughts?

I really love my ML320 even though it has 250K and the plastics are starting to crack and break. I'm committed to getting 300K before I get a new vehicle.
 

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2000 ML55 sold😢 2013 ML500,😁 2015 C250 estate wagon, 1927 Dodge 4 sedan, 1929 Dodge
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I'm excited to give it a try. Did you pull the manifold to insert the tube or did you work some micro gymnastics to get the tube in while the intake was on the vehicle?
It’s definitely easier to do it with the manifold off. I can’t recall when I did it with the manifold apart or before I did that.
Try Witek’s fix there it looks perfect.
 

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2002 ML320
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Discussion Starter #15
Repair hose is available here:

Thank you for the link to the line. I'll order it. One a couple of questions still remain. Can I replace the line without opening the intake manifold? It doesn't appear that I can. If I have to split the intake manifold, should I just use gasket sealer when putting it back together since a gasket is not available? Thanks again for your time.
 

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The manifold is glued together it’s difficult to get apart.
Wait until you get the repair hose.
The genuine hose is replaced by pushing it from the inside out. It has a large taper holding it in place.
 

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2002 ML320
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Discussion Starter #17
Thank you for the link to the line. I'll order it. One a couple of questions still remain. Can I replace the line without opening the intake manifold? It doesn't appear that I can. If I have to split the intake manifold, should I just use gasket sealer when putting it back together since a gasket is not available? Thanks again for your time.
I read the description. It appears that this is not the OEM hose, but a repair hose (might be similar to what mattml430 suggested). Also, looks as if doesn't require splitting the manifold.
 

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2002 ML320
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Discussion Starter #18
The manifold is glued together it’s difficult to get apart.
Wait until you get the repair hose.
The genuine hose is replaced by pushing it from the inside out. It has a large taper holding it in place.
Good suggestion on waiting for the repair hose. I've been driving for 30K like this. Another couple of hundred won't matter.
 

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2002 ML320
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Discussion Starter #19
I see I'll need the intake manifold gaskets. Does anyone have the part number for the combination valve gasket that will also be needed for the replacement?
 
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