So my wife came home from work and we hopped in the R and went to the market. Long and short we were leaving and came to a stop light when I felt what feels like the engine is shaking while the car is idling and my foot is on the brake. Hard to explain as I expect any MB product to behave in a silky smooth fashion in this situation. There is a subtle but rapid knock, it's very faint and you have to squint to hear it or notice it but IMO not a normal characteristic of the car, if you know MB's at least newer ones you would instantly think something is not right with our car.

Brief history we owned a W204 C300 with the same motor just slightly smaller and it's motor was silky smooth up to the 46K miles we put on it in two years. Also my dad has a new 2010 W212 E350 with the same motor and it too is silky smooth and doesn't behave this way. Anyway I still love this car but will be taking it in this week while still under the CPO warranty to hopefully correct this and a small list of other items 1-2 jerky downshift, and sometimes the power lift gate sucks in and sometimes it doesn't not sure if that's normal or not?. I'm thinking maybe we got a hold of some bad gas? we always use 91+ octane that's the highest grade we get in California, I'm worried maybe the prior owner used a low grade of fuel regularly. Just a side note when we test drove our car before we bought it, I thought the idle was slightly rougher than some of the R's we had driven, even more so than the somewhat beat up one with higher miles we drove a few minutes prior. As soon as the car was ours I had my wife drive out the tank of gas and I filled it with 91 octane and 20 oz of Chevron Techron concentrate plus fuel treatment. The car began to run like a new engine after that. For some reason the rough engine feel is back and I hope they can find a solution. Also Wife says the 1-2 downshift bucking in the parking lots is giving her a headache so hopefully MB can cure this for us too. Our car just turned over 27K miles this week.

 

Lower octane won't cause rough running. Just lower power as the computer will adjust the timing to prevent "knock".

Maybe the fuel filter needs replacing? Injectors clogged? Bad coil pack?

 

Does it do it all the time at every stop/red light when you come to a full stop?
Or is it an intermittent problem? Also, does it feel as if the motor is about to stall and then the RPMs go higher because the computer sends gas to keep it running? (just like as if it was a manual transmission and you had released the clutch when fully stopped and in gear, and then you gave it some gas so that it doesn't stall). Does it last a few seconds and then it goes away?

I am experiencing that with my R500 very infrequently. I had taken it to the dealer eight months ago because I also had the rough shift from 2 to 1 gear. They had replaced the valve body and it took care of the rough shift, but the problem you are describing is still there, just not that often.

I would appreciate you reporting to us after you get it back from the dealer.

 

Dropped it off today, our very friendly service adviser thinks it might be the valve body causing the rough 2-1 downshift at low speeds.

My rough engine however is only at idle when the car is in drive and your foot is on the brake holding the car. Example stopped at a light, stop sign, parking or in the driveway. There is a constant vibration and audible humm from the engine, if the hood is popped I can see the engine vibrating. Just so everybody doesn't think I'm weird (Yes I know engines vibrate) But I can see it vibrating. The 3.0L on our W204 although vibrates naturally as well when Idling (I can't actually see it shaking or vibrating) just feel it ever slightly. On the R I can both see it and feel the motor vibrating abnormally so I am concerned. Our SA thinks motor mounts but I not sure on that.

I think a stuck injector, dirty or bad injector, mass air flow sensor, O2 sensor or relay. Hard to say, possibly bad gas. Some might think it's normal but IMO a $50K+ vehicle should be silky smooth at all times. Heck my Chevy truck doesn't do this at a stop light so why should my R350 right? Of course the rear hatch didn't want to act up when I was showing our SA but maybe it will while they have the car in their possession. I will report after picking it up.

 

Sounds like the motor mount issue that is common on the W211 platform. The mounts are fluid filled and sometimes leak, causing what appears to be rough idle, or misfiring cylinder.

 

it sounds like a miss fire

 

Got the R back today and while all the paperwork says "Cannot duplicate customer concern" for rough idle, hard 2-1 downshifting transmission. My SA said my car needed two updates of which software ME-SFI was outdated and needed to updated. My SA said they flashed the computer for the transmission & Engine roughness and on my 20 mile drive home I honestly can say the car did not give me a rough or hard kick or buck. I drove it in a parking lot for 10 minutes under the same circumstances when it would buck and jerk before and it did not do it once, this is good so far. The rough idle has diminished by about 80% I can't really hear the audible humm like I did before, but I can feel, a subtle click through the steering wheel that is in tune with the engine speed at idle. I didn't notice this before but it feels better than it did. They also said of course they could not duplicate my issue with the intermittent power lift-gate sometimes sucking in and sometimes just closing hard. But did say they aligned the striker and it hasn't messed up yet. Wife will drive the R all next week so we will see from there. All and all it feels like new again so we will see.

 

Great. It is good to hear that your R drives better than before the software update,

Can you tell me exactly what software written on the invoice?
Last time I test drove my R with mechanic foreman and he told me that it is normal on the hard 2-1 downshifting transmission.

 

I had similar problem and I waited for 2 months for newer software. It was a huge problem with the latest release and it caused to stop updating software from month or so until fix came from Germany. In addition to programming my TCU (transmission), I did ECU as well. Also, I have asked SA to perform 'transmission adoption reset' (it does reset to factory setup and you start fresh - in other words, new learning curve for transmission).

I paid 1 hour for service and it did worth it ...

A