Fluctuating Tachometer
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,142
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
Why has not anyone confirm yet this RPM fluctuation using a 2nd digital gauge OBD2 type vs the mechanical tacho at instrument cluster ?
If there is no mild jerking or any mechanical feel that indeed the engine has fluctuating RPM, it could be the tacho itself fluctuating its value.
OP did not mention he felt a kind of engine "hunting" of 100 RPM , he kept mentioning only visual value of the RPM.
If there is no mild jerking or any mechanical feel that indeed the engine has fluctuating RPM, it could be the tacho itself fluctuating its value.
OP did not mention he felt a kind of engine "hunting" of 100 RPM , he kept mentioning only visual value of the RPM.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,142
Likes: 1,293
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
Then, I don’t see mention if this fluctuation happens with the cruise control ON (or I missed it). I assume it is with CC so if the car and engine is fluctuating then is it because the CC is telling it to do it?
This leads to look into the speed sensor the CC use. Is it some type of combined speed reading from the wheels speed sensors or is it the reading from the transmission output shaft? I’m guessing CC reads the speed from the transmission output shaft so that sensor would be what I would look at. Or just the harness connection to it.
I haven’t looked but it might be just to disconnect/connect the harness to all electronics to the gear box. I don’t know where this harness is but I wouldn’t think it is too difficult to reach.
Output shaft speed sensor itself I think is inside the gear box but I’m not sure.
Out Of Control!!
Joined: Apr 2019
Posts: 11,993
Likes: 6,827
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
narrowing things down a bit...
@OP... is your problem with the engine rpm fluctuating -or as the title say bouncing tach ??
🤔
+++++ answer:
- The engine rpm does go up/down
- Tach is A-OK.
- Vacuum leak, breather vent involved.
✌️
🤔
+++++ answer:
- The engine rpm does go up/down
- Tach is A-OK.
- Vacuum leak, breather vent involved.
✌️
Last edited by CaliBenzDriver; Aug 18, 2023 at 03:16 PM. Reason: few answers
Newbie
Joined: Nov 2021
Posts: 1
Likes: 0
e350 w212
I recently purchased a 2011 E350 with around 61,000 miles and I noticed that the tachometer will fluctuate up and down about 100 RPM. This happens while driving at a constant speed and with steady throttle input. I saw a old post on here that described a similar issue but I'm not sure what they found. I dropped it off at the dealership this morning for diagnosis. I will post the findings when I hear back from Mercedes for those who may be suffering from similar issues.
Good day
I also have a E350 it is a 95 reg with only 23k on it. I just got it a few months ago. I have been driving it on the motorway and notice the same problem. In the end did you get it fixed? If I shift down for the engine to do over 3000rpm it stops.
Newbie
Joined: Dec 2021
Posts: 11
Likes: 4
C300 Benz 2011 4matic
I'm also interested in finding out if this problem was fixed and if so, what was the actual problem, i just bought a 2011 E350 and while driving i noticed the same issue where the rpms go up and down while driving at a steady speed, is not very noticeable but I can feel the car speed fluctuate by the same amount and I can hear the car jerking up and down as well.
I have read many other posts and I am beginning to lean towards a transmission issue, i have read somewhere this is a very common problem with these cars, i read somewhere also that it might be a bad solenoid, there's no error code or anything, I bought a very nice scanner which can read and control most of the control modules in this car and couldn't find any code related to the transmission.
It would be very nice to hear from someone else with a similar issue before I decide to drop the transmission myself and try to investigate in more detail what's going on.
Walter
I have read many other posts and I am beginning to lean towards a transmission issue, i have read somewhere this is a very common problem with these cars, i read somewhere also that it might be a bad solenoid, there's no error code or anything, I bought a very nice scanner which can read and control most of the control modules in this car and couldn't find any code related to the transmission.
It would be very nice to hear from someone else with a similar issue before I decide to drop the transmission myself and try to investigate in more detail what's going on.
Walter
Newbie
Joined: Aug 2023
Posts: 3
Likes: 4
C220
Fixed
My cdi c220 had the same issue and I've been searching high and low for the answer. I never found it online, and I rarely post things on forums, but I feel like I can help many people out with this simple solution. I'm sure there are other reasons why revs can fluctuate but for my c220 the problem was that I had a vacuum leak through the engine oil dip stick.
THE SOLUTION was a 2 cent rubber O ring around the top of dipstick lol. I hope this helps a few people out.
THE SOLUTION was a 2 cent rubber O ring around the top of dipstick lol. I hope this helps a few people out.
Newbie
Joined: Feb 2021
Posts: 1
Likes: 0
e350
Mercedes dealerships service department are thieves and liars
I've had my car into Mercedes twice in the recent past to replace a fuse only be charged $300 I've had the same fluctuating tech. I have had the same problem for a little while and I've had no results with that as well. Questioned why is my car sputtering or hesitating at about 2,000? RPMs has anybody had to replace the donuts in their exhaust? And I am also having to charge my battery about once a month or it'll die on me more often than that even.
Newbie
Joined: Jun 2024
Posts: 1
Likes: 0
2011 E350
I recently purchased a 2011 E350 with around 61,000 miles and I noticed that the tachometer will fluctuate up and down about 100 RPM. This happens while driving at a constant speed and with steady throttle input. I saw a old post on here that described a similar issue but I'm not sure what they found. I dropped it off at the dealership this morning for diagnosis. I will post the findings when I hear back from Mercedes for those who may be suffering from similar issues.
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