C350 (2010 W204) - cold start - a few questions

Page may contain affiliate links. Please see terms for details.


Jul 18, 2023
HI all!

I have just picked up a C350 yesterday and so far i absolutely love it! Its a 2010 C350 with 133k. I have a couple of concerns;

1) Today was the first cold start i've had with the car, and i noticed that when it idles from cold - there is a very slight intermittent wobble or shake - again its very light and intermittent, but definitely noticeable - The revs stay ok and dont fluctuate - car starts fine and idle seems perfect? Just the weird intermittent shake

2) When i set off from cold start and in slow traffic, the gear changes at low speeds from 5-15mph seem to be a bit lumpy? I was going uphill through town at about 5mph and although my foot was fairly steady - there was a noticeable lumpyness to the way it drove at low speeds - the revs seems to bounce very slightly

Both of these issues are only when the car is started and driven from cold - when warm its absolutely fine

I have purchased some Wynns Extreme Diesel cleaner to run through the system - after reading other threads this seems to help

Any suggestions? Or is this all normal?

Thanks again :)
Just to update a little.

I purchased an Icarsoft i980 and did a scan and it said no fault codes which is a good start.

So I did another cold start today, and monitored things. Its not rough idle, its more of a slight shake.
So I tried was putting in in D (still on driveway, not moving), and as soon as I did this it was absolutely perfect, no intermittent shake.

Set off, and gear changes seem to be smooth.

Its going in for service and check over so I'll update if they can diagnose why it shakes a little when cold in P.
just to update this thread:

Just had the car serviced and full check over and investigation into the jerking issue.

They have advised me that one/or more of the injectors is more than likely spraying incorrectly for the cold start procedure, and this is causing a slight miss fire, and causing the car to shake and jerk when cold.
They are rebooking me in to have all 6 injectors removed and flow tested and replaced where necessary
One thing i have got is some Wynns Xtreme Diesel injector cleaner. I'm gonna put a bottle of that in tomorrow and see if that helps too
ok so just to update this:

Car went to local mechanic - said its likely injectors
Car then went in for recall at Mercedes - got them to have a check and see what they think - they said engine mounts - they then said as i was collecting - possible injector starting to fail
Mercedes then did as free health check and one of the things they said was the orange turbo seal (found on the plastic maf unit) was split - and they said the actual plastic that connects to the turbo is cracked

Ok so i ordered new part (not mercedes as they wanted 750 quid!)
Part arrives and i fitted at home - 10 min job, easy

I then noticed that a vacuum pipe was just hanging down, and was split and not connected - so i managed to find out where it connects to, cut off the split section and re connected it

Started the car up from stone cold (expecting it to still be lumpy)
But it was absolutely perfect! - no jerks, no lumpy running - absolutely smooth as!

So I'm not sure if this is 100% cured - could just be a bit of luck
But it does look promising

Here's the old MAF housing - pretty beaten up!

here's the pipe i found disconnected - had a bad split in it too! So i cut off the split section and re fitted

here's where i re connected the pipe
Do you know what that vacuum pipe was for? I have a similar split (seems to be a common problem) and it kept splitting so have silicone taped it. What’s it for, where does it go… does anyone have any idea?

Do you know what that vacuum pipe was for? I have a similar split (seems to be a common problem) and it kept splitting so have silicone taped it. What’s it for, where does it go?

I have no idea if I'm honest. I saw it was just hanging down and the I saw the T connection with a missing hose, so realised it was from there. (My hand points to the T connection it had come off)
Yer mine was badly split too, perhaps an aftermarket vacuum hose may be better?

Users who are viewing this thread

Top Bottom