So my car was having the rotten egg smell after driving in traffic then spirited last segment.
I had this in the past with my Alfa Romeo and that turned out to be a intake manifold gasket folded over.
So I checked with an obd2 scanner the long and short term fuel trims.
It was positive and during driving in the single digits while after in idle it could go all the way to 18-20 %. Still below the code threshold.

Also don't believe what you see with googling the smell, it's not a rich, it's a lean condition.
When in doubt use the trims to see which it is.

Also, don't jump into replacing the converters.

So anyway, meanwhile my gas mileage is at best 14.5 and worst 12 MPg.

So I started to think that it may be a good idea to check the intake manifold.
As I pulled the intake tubing, I saw brown residue around the manifold bolts. There were some leaves and debris there too.
So I decided to check the torque of the intake to heads 10 bolts, using the tightening sequence in the wis.
so they were all under 10 Nm, I corrected this and then gave them another 45 degrees, as opposed to the factory procedure, which wants first a 90 degrees and then another step at 10 degrees.
These aluminum bolts were already stretched once and I did not want to take a chance with them.
With the 45 degrees none snapped.

So once this was done, I did a quick drive and the smell was gone, then commuted to work and saw single digit trims no matter what I did, after I was done and in idle.
I started to see negative trims too, with the short term and cruising with long term trims for a while in the 1-2 % range
Then I started to notice that the mpg computer started to indicate an average of 16.8 MPg, a number that I never saw before indicated.
In addition to this, a hesitation when starting from idle is gone.

I will buy the gaskets and bolts and replace them, but for now, the outcome is good.

 

When I replaced my intake mani gaskets, a couple of the bolts were only finger tight. Definitely a good idea to replace them.

 

I already have this down to check over the winter. My car is 5 years old now so I figured it might be a good idea with the number of posts about loose manifold bolts. I also have it down to check my accessory drive belt and pulleys as these seem to cause problems as well. When the belt breaks it often seems to cause other damage with torn wires. It is a good idea to keep an eye on these known maintenance issues that are not part of MB Scheduled Maintenance.

 

12mpg is great ..thats like average ..i barely get 10 ..most of the time 7-9mpg

if you have any sort of exhaust work - it'll stink horrible

the intake manifold won't give off any smell ..in fact you probably won't even notice theres an issue with it until you're sitting there one day wondering where the F that loud whistle is coming from

how lean do you run? you can easily tell if you run lean or rich by the black soot on your tail pipes

 

Once the gasket is compromised I doubt re-torquing the bolts will help. Didn't work for me.

This is what mine sounded like (when hot) before I replaced the gasket/bolts.

 

^^ this ...thats exactly how it sounds ..very obvious

 

My car is stock. I should be able to get better than 12. And I AM getting better than 12, I did not empty the tank yet but looks like with all driving conditions being equal, I am going to be moving to 14 mpg.
As far as soot, probably by the time you're looking at soot, if you're still stock, the converters are gone. As far as lean, I am not used to reading lambda but afr (my obd2 readings are lambda). Of course I could calculate afr from lambda but am too lazy and besides looks like I fixed it, for now at least.

As far as the gasket, I don't know what you can and can't do with it, but I certainly see my new fuel trims and gas mileage. Also the bolts being loose can't be good for sealing it.
But yes, if the trims go bad again, I will buy a set of new bolts and gaskets and replace all. This has not cost anything so far, so I will use this while it lasts and post when it doesn't anymore.
As far as the noise, my car was not yet at the point where it threw a code. So maybe to early for noise too.
I think the code for lean may happen when the sum between the sort term and long term trims for a bank breaches 25%. Maybe that's when it whistles too.

 

The IM bolts and gaskets are cheap. This is a known issue, they revised the bolts. Why not just do it properly instead of crossing your fingers?

 

https://mbworld.org/forums/c63-amg-w...valve-diy.html

 

That's what mine sounded like too. And then at WOT it sounded like supercharger whine.

 

I am not disagreeing with you.

My first priority Is to buy the star Das testing rig. I may do this next week.
Then I will change my transmission fluid.
Then I will look into the gaskets.
While the manifold is off, I would want to change that breather/pcv hose and bring the injectors to be ultra sonically cleaned and flow tested to South Bay injectors.
Then I need to get a set of top, and bottom injector seals, it adds up.

However, if in the future I decide to do the head bolts, only with head gaskets, I would need to replace the manifold gaskets and bolts again anyway.

 

I'm starting to buy the items to replace the manifold gaskets.
So, I started to wonder why Mercedes used Aluminum bolts, to fasten the manifold.
Cost, weight, galvanic corrosion protection, the ability to sell the same bolts again, as they become one-use?
Turns out that galvanic corrosion is a big factor, but also the large coefficient of expansion of the Magnesium alloy, which the manifold is made out of. Steel could not match this, Titanium alloys would be terrible.


Here's a white paper from Kamax.


http://www.kamax.com/fileadmin/user_...ning_of_mg.pdf

 

I finished replacing the gaskets.
I had a problem with the vinyl line that goes from the manifold to the brake booster, the plastic elbow that goes into the manifold snapped.
In retrospect, I would disconnect this by the firewall, where there's a nice fitting, not try to pull it out of the manifold.
Then it only took ... a long time to get the replacement.


As I was testing the work I also got a light for VDC ABS and a check engine light for the throttle sensor/actuator. I think all 3 are related and I think one of the connectors for the throttle was not seated right, when I reconnected it.
So I made sure I heard the audible click on both throttle connectors, reset the light, drove it around at various speeds, looked at the trims, all clear.


I also replaced the PCV/Breather and took apart the old one. It's just a spring loaded flapper in a can. Looked like it was working anyway and it was not full of oil or gunk anyway.


I decided to measure the manifold Aluminum bolts, new vs stretched, I'll post pictures.


Unrelated, I also replaced the power steering fluid.

 

The power steering makes a moaning sound and apparently needs fluid pretty commonly...


PCV valve also needs replacement strangely often. On my 2009 C63 I had it changed twice within 4 months by dealer.

 

My Mercedes background is of two W126 and a W124. Those have a filter in the powersteering fluid can. You change the oil and the filter and get rid of a low powersteering buzz, not the low fluid loud moan.


And this is what I was trying to do here, also a more uniform steering feel.


The PCV I had this opportunity for an easy replacement, so I went for it.