draculr

I've got a 2013 E400 W212 (Australian spec, I don't think it was available in the US. It has the M276.8 twin turbo 3.0L V6). The car only has 68,000km (42k miles) on it.

On a cold start it can be quite lumpy as the revs start to drop it's RPM down to it's regular idle range. The tacho also seems to step down rather than smoothly go down in RPM during this phase.

It was doing it before and after I replaced the spark plugs and there are no codes.

When it's settled to it's normal idle range and when accelerating it is very smooth so I don't think it's the mounts. Anyone have any ideas?

S-Prihadi

USA I believe got E400 as is 3.0 Turbo M276.820 engine only in 2015. This is because when I use FCP Euro for my engine parts, I must use model year 2015.
My country Indonesia got it in as model year 2014 and sold in 2014, year of manufacture of my E400 is Aug 2013.

You need a proper good scanner if you want to start the troubleshooting, best would be a clone but FAST Xentry like the one from Benz Ninja, so that you can custom configure many PIDS
or data perimeter and get 2-3 Hz logging speed .....to "catch" this cold start combustion related issue.

Describe accurately the time frame :
At 30C ambient temperature...from start of engine cranking and engine actual firing to its normal 600 RPM stable would need sometime, approx 120 seconds.
Where in this 120 seconds region your engine doing the "lumpy" engine idle ?

Here is an example for some PIDS you would want to show during the troubleshooting. See that in 120 seconds before I reverse my car a bit, my M276.820 engine will be idling at 680ish RPM. Ambient temp was 31.5C.


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There will be more specific PIDS if in your case, like Lambda sensors value and its heater value, manifold intake pressure aka MAP, Fuel System Close-Open Loop, fuel vapor % and so on.
What you want to hope to catch is : the anomally or some sensor "hiccups".

draculr

Oh, good to know I can search on fcp using the 2015 MY! I wonder is there anyway I can use my iCarSoft MB scan tool to pick up the issue? It has some data values but you can only see 5 at a time unfortunately.

Maybe it's because it's quite hot in Australia at the moment but my car settles to 600RPM fairly quickly. The lumpyness happens only about 10-20 seconds after starting the car up and it settles to 600rpm very quickly after that and it becomes smooth.

I tried starting my car up this morning with no fan or A/C running and it didn't have the lumpyness on startup. I wonder if it's to be expected that the A/C running during the first 30 seconds can exhibit this symptom? I'll have to try again a few more times to confirm that it never happens while the A/C is off but I do need to wait until the car cools down for a long time between testing.

S-Prihadi

well, during a cold start ..... it is on purpose the ECM would make a richer mix of fuel.
If your front lambda sensor wide band has a good heater, it takes under 10 seconds for it to warm up to 400C and start to assist in making
engine get a proper AFR or in a close loop system.

icarsoft is too slow and that 5 data pids per page will waste your time since you must do cold start to test.

As I recalled, the ECM would use the last engine kill fuel trim as basis for cold start fuel mapping on next engine start.
If ECM loose power ( say battery disconnected on purpose or very weak battery) before the next engine start, it may reset that fuel trim and the first few seconds on engine run is not as smooth as it can be.
How old is your main battery ?

S-Prihadi

Something very important I forgot to ask.

AA. If this car is new to you and it has this problem as-is when you bought it, you have to let us know the history.
BB. I am assuming this car been with you for sometime say 10,000KM or more and been like 1+ years and all was good and dandy, and then suddenly you have this issue you
are discussing.

Which one is your story ?

Since W212 is getting old and cheap, many jump into W212 ownership.
Used car can be good one or on the unlucky spectrum could have been maintained by stingy-bas-tardz-dumb-*** 2nd or 3rd owner and you are the unlucky 4th owner.

If ever one shares his "issue", the car history must be informed well ahead, as you wont believe the kind of non-sense a stingy-bas-tardz-dumb-*** 2nd or 3rd owner
could have done to the car.

BTW, what MB genuine spark plug P/N are you using ? What torque value did u torque it to ?

draculr

It's new to me as of about 3 months, but I only started to feel the issue as it got warm so it's potentially the A/C running harder on startup that's doing it. I'll try a few more days of cold starts without the A/C running to see if it's isolated to that.

The car has a very, very good history however. It was owned by one 75 year old and always serviced once a year at the Mercedes dealership. He only ever did 6-8,000km between services and did all the extra services that were required such as the Automatic Transmission Fluid.

The spark plugs I used were part number A2701590600, torque to the correct spec (I believe it was 23nm from memory). I did that job myself.

S-Prihadi

I hope your icarsoft is not MB V2.0 or similar older unit, like what I had : https://mbworld.org/forums/e-class-w...sing-unit.html

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Find M276 3.0 Turbo good information booklet. Read it well.

You can do this basic test first.
Make sure car engine has stabilized to room/garage ambient temperature and is shaded from sun as being better.

Do not start engine, simply ignition ON.




Read 3 available temperatures data :
01. Ambient temperature at front bumper left side.
02. Intake Air temperature, for your engine this sensor is at the aftercooler in front of the engine, blocking your access to main pulley. B17/8.
03. Engine coolant temperature.
If all these 3 is within 1.5C of each other, that is good news.

Read 3 available pressure data :
01. MAP , manifold absolute pressure. This sensor is called B28/7
02 & 03. At the air filter housing, 2 pressure sensors B28/4 and B28/5.
They should be within 3-5% of each other as per atmospheric pressure of your location / altitude.


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Go back and see the video I linked of my engine.
See how the Exhaust VVT during cold start will do for its actuation.
Your VVT should mimic that for a cold start and at the speed of what my VVT is doing/responding.

Some reading here on GDI engine cold start strategy:
https://digitalcommons.mtu.edu/cgi/v...0&context=etdr

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Things to observe when engine being crank to engine running for that 20 seconds you speak of.
01. How fast is your rail pressure building up to 180-190 BAR.
02. How big is your throttle body opening ?
03. All other parameters in respect to combustion process, look at the PIDS.


Our HVAC is a smart variable displacement compressor.
If your engine is OK, that compressor can not ruin your engine good idling upon starting up even with HVAC ON.
HVAC ON is what you think you did, true swash plate activation is up to the ECM which has final say for HVAC Compressor % activation and also ECM
has idle-up feature for HVAC engagement, including extra fan speed request.
Also our engine low torque is so good, HVAC compressor is not a bother for it.


Have fun troubleshooting.....