An ECU gremlin

+1 Have they completely reflashed your ECU unit? If not try that, if so, ask for a new ECU.

So you guys really think it the ECU needing to be reflash, or is it a suggestion. And BTW "ECU gremlin", might be a silly question but is that another way of saying it could be an ECU issue? Can we reflash the ECU ourself? Thanks

I hate to tell you this...
 

I have a 2 week old 2010 C300. Does the exact same thing, the tach needles moves a little bit "dances up down ever so slight" specially at low rpm under 2k and with light throttle.
I don't hear nor sense any surging in the engine and the car speed is perfectly constant with constant pedal pressure.
It does not bother me one bit, and I will not have the local gorillas at the dealership tearing all over the car.
I don't think what you have is a problem, could be a design flaw more than anything else in some electronic component.

I drive on the highway most of the time on cruise about 70-75 and because I am on the cruise I see the needle dances a lil bit, sometimes one whole tick and sometimes less than a tick. What you are describing to me sounds exactly the same as what I have, no surging, speed is constant. Gtechy, does your car do it somedays and it doesnt? Wouldnt a design flaw in the electronic component be bad? Should I still ask the dealer to get my ECU reflash? I am currently at 12k still trying to figure this out, besides the first time when I had my car, some pins were loose created the tach needle to be really jumpy.

I think my car does it all the time, it is EXACTLY the same as the video that was posted on this thread. Again, since the car drives smoothly, I don't stare at the needle.
It does not bother me much. I am pretty sensitive to how the car/engine/steering are working but on this car, I just don't detect anything not working right in terms of how the engine is running.
I think it is up to you, but it looks like they have gone over the car, the ECU, codes, etc. and replaced parts to no avail. Do you really want them to keep tinkering with your car, if there is no driveability problem?

The video that was posted here had bouncing needle at idle position. Mines is only during driving, but you are right!, it does not affect driveablity at all. I am just worried if there will be any long term future effect, but it is good to know that I am not the only person that it is happening to. I guess it is "normal".

What does an ECU reflash do?

I looked at what the needle was doing on my car....completely still. (I have 30k on the clock) After acceleration, Park, Neutral, etc. It doesn't bounce around like the video shows.

I have a few theories: bad O2 sensor, mass air flow sensor, or some other sensor along the exhaust system.
Another theory is that your car may be brand new - and it may still be in it's breaking-in stage.

Something is compensating by putting more fuel or air - result is a slight increase in RPM, which is what you are seeing.

How many miles are on your car? And which Northern California dealer did you work with?

...Doh! Just read that you have 12k on your car. So my guess is that its a bad sensor.

I have worked with the Stockton dealer (berberian motors), very good service dealer. They have tried multiples times on my car trying to find out what happen including changing a crankshaft postion sensor (not sure what that does). But maybe I can recommed something to my SA. So now I am guessing that a reflash in the ECU is not needed. Any suggestion would really help, I think the o2 sensor or the mass air flow sensor sounds like a reasonable reason but wouldnt a CEL come up if the any of the sensors are bad?

After 3 years, Looks like Mercedes has not rid the problem.
I am having the same issue on my brand new 2013 C300.
During steady drives, the rpm would play up and down.
Also when you step on the throttle lightly and then release, and then step again lightly,
I notice that the rpm needle is climbing up but its very choppy.
Seems like it is out of breath or surging if you call it.
I never experience this kind of issue in my life, whats worse this is a brand new car.
I am still waiting for the dealer response on this issue.