i have noticed that my RPM gauge needle played/pulsed when idling. in other words the needle would never stand still and seemed to rev up slightly in intervals.

well i though it was just the dashboard cluster but i now notice that the engine is actually speeding up and revving ever so slightly, but enough to feel and hear it.

anyone else get this or have any idea what causes this?

(2009 C300 4matic 5000 miles)
thanks

 

Does it do it while in park and/or in gear? Do you have the AC compressor on? What kind of RPM difference are you seeing and how quick does the puse last and how often does the pulse cycle?

 

the fluctuation occurs in the below cases:

Park, drive, and reverse with brake applied.
Neutral: brake on and off
A/C: on and off
Aftermarket HID: on and off

In all the above cases the RPM pulses. it seems to come in waves as some moments the car runs perfect and needle idles at a stand still.

the fluctuation is upwards and can be a whole tick mark on the tachometer. last night it jumped almost two tick marks and the car sounded and felt like it was revving.

the pulsing occurs almost anytime you look, but feeling and hearing is hard if at all possible to do most of the time.

the needle has been flickering like that since i got the car but i didn't notice until after owning it for a week...up until last night i never felt or heard but not i can pick up that the engine is actually spinning up when i focus

 

also, i have taken a video and will post tonight.

i pulled up some diag codes from the engineering menu and found the two below occur every few minutes.

01-4c-20780
01-4c-08106

i called the dealer and service would not tell me what these numbers were, they also said that unless i get an engine light i should not worry...haha

i described my issue and the service guy expressed no major concern

any help would be appreciated though...
thanks

 

here is the video of the rpm needle playing-
this is the usual movement...sometimes less obvious sometimes more

car was in park, A/C on, in this video

 

My C220 CDi did something similar when new. The needle would move up and down over a range of about 50 revs all the time when at idle, in both C and S mode (although I could not hear or feel anything from the engine).
It stopped doing it when I had travelled over about 4000 Kms. The needle is now dead steady on about 750 revs in C, and 850 revs in S mode.
If your car is brand new, it may settle down as well after you have travelled a few miles and the engine is "run in."

 

This is not normal, despite what some service advisor says. They are not nearly as smart and well informed as they hope you think they are.

Ask to meet with the MBUSA rep which may stir them to action.

 

My dads Porsche used to do that, turned out it was a faulty air sensor/regulator. Once replaced it was fine. But it was way much more extreme than that and only when the engine wasnt warm enough. Is it even after youve driven for a while or only when you just start driving?

 

Looks like it is idling a bit low. Mine idles about 700RPM and is quite smooth...except for the start up woble. Anyhow, there is definitly something going on. Service visit time.

 

by the way the idle has this problem whether engine is warmed up or cold start....
i will go ahead and take it in to dealer soon.

does anyone think that my aftermarket HID kit will be an issue? should i remove it?
i have done my best to hide the HID kit and unless you look up front at that area it is very hard to spot them.

any such experiences at dealer??

thanks to all

 

as an update....

the family recently took possession of another silver 2009 C300 sport 4matic and it seems that this one has the exact same jumpy RPM needle.

i still have to check any other aspects but from first glance the reverse and acceleration lags are also present...

 

any updates on this issue?

 

i am a dealer and this is not normal - i have never seen a car do this in my entire career.

whatever dealer you go to is blowing smoke up your a$s...don't let them bend you over backwards on this one...

if they don't act, just keep on calling the CAC and remind them weekly about how your dealer won't fix your car in accordance with his dealer agreement.

good luck - it's too bad we have stores like this out there that stain the name of the brand.

 

What is CAC? Is it some sort of customer care number that we can call.

 

I had this on my old Peugeot, but never on my Merc. It's typically just an idle adjustment, or it could have something to do with your air or fuel system / sensors or maybe even slight fouling in the ignition. If the engine senses it is stalling while idling it will give a small boost of fuel to compensate. When the needle goes back down, it will repeat the process. Then end result is the needle bounces while idling. It's nothing drastic, but can put a significant dent in your fuel consumption. My merc runs a solid and smooth 500 rpm when idle. What grade fuel are you using in the car?

EDIT: Added question

 

I am using 91 from the start even since i bought my car. Umm somthing this simple and my dealer has to email MBUSA for an answer. I should hopefully get an answer by this coming week, and also be checking with my local dealer that I have here. I bought my car from out of town.

 

Slight engine hunting can be caused by a defective O2 sensor. Does the engine ever stumble slightly on acceleration?

 

yeah - the customer assistance center

1800 for merc (i believe)

 

actually the cars driver perfectly normal, no hesitation when puching the gas or even at idle, it just the rpm stick fluctuate a lil bit.

 

So for a couple of days now, the dealer still have my car. They said that becuase it a new car and that they have not yet to approach this problem, so they are email other dealers and MB to see if any other dealers has had this problem and how to fix it.

 

Brand new cars have all sorts of weird things happening. Mine drove like a pig and seemed to be completely defective until 6000 miles and a software update. Then it felt like a completely different car; snappy, smooth, less fuel etc.

Don't sweat anything in the first few thousand miles unless sounds / looks catastophic.

I strongly suspect there is running-in software mapping that auto expires after a certain mileage based on my experience and those of many who have described many odd / unsatisfactory charachteristics of their new MBs.

 

Email. Where are you, Lapland?

The fact is that all the techs have a computer terminal running off the MBUSA server. They can, just like we do in Google, type in a keyword or two and a long line of entries from MB dealers around the country pop up dealing with any problem you can think of. Saves them wasted time and throwing parts at it, hoping to get lucky.

 

Alright, Just got my car back today and it is now fix perfect. They have tried many sorts of type of diagnostic including changing out the instrument cluster, all came up to be some pin being loost from the control unit (ECU). So who ever is having this problem, just have the dealer check that out.

 

Damn - good information. We have seen that on a couple of W203s

 

Ok, so I am having this minor issue again, before it a was a bit harsh. The thing with my situation is that is only when driving, especially when cruising because I am at a steady speed. The needle only fluctuate intermintly and is not on a consistent base so it pretty hard to show it to the dealer. I have had them take a look a few times but they just couldnt find anything wrong with the car, including changing out the cluster. They hookedd it up to there DTC and everything. THey have also tried changing the crankshaft position sensor. Do you guys know anything else that can cause this RPM needle to flucuate?