Davis_C320

Well I have an 04 Mercedes c320 4matic that for awhile, when sitting in drive and ONLY when cold, the whole car vibrates, can feel it through the seats. At this point, the car feels like it has too much power at idle and the car moves quickly on its own when I release the brake pedal. I've replaced engine and trans mounts, alternator, plugs, front axles, all fluids are correct. Thinking maybe a vacuum hose or crankcase hose. Again as the car warms up the vibration goes away. Any answers?

RCPDesigns

I replaced the valve cover gaskets on my daughter's C320 over the weekend. As part of that task I replaced the breather hoses. They are a pain and require removing the MAF and fuel line from the injector rail. The hoses were not broken but they can be hard to get off the valve covers with damaging them. While going through the procedure I noticed that the MAF gasket/o-ring was not making a good seal at the top and, in general, the whole assembly was a bit oily and dirty. I cleaned all of that (didn't touch the sensor itself as it looked fine) and put it back together.
I also found that quite a bit of oil had gotten in the back spark plugs as the valve cover gasket was leaking. I cleaned out the spark plug boots.
Once everything was back together I do believe the engine ran a bit smoother.
My guess is that cleaning out the MAF and getting the gaskets sealed tight probably improved the idle performance. Very hard to tell, but you've already done all the things I would suggest. The valve cover gaskets do like to leak so maybe give your's a good inspection and see what you find.

Davis_C320

Do you think that this could be a problem only if it's cold? Seems like if any of those, I would see the issue no matter what temp the engine is at...I also have heard these valve gaskets are prone to leaking...but when driving the vibration goes away after about 5 mins

RCPDesigns

I really don't know, but my daughter says that her car is now smoother when it is first started and 'doesn't make that sound'. I have no idea what 'that sound' is as I've never heard it. You've done the normal things for a vibration. My next guess would be the MAF and if you're going to take the MAF out and clean that area, I'd replace the breather hoses. If you're doing that, you might as well check the valve cover gaskets and replace those if needed.

Really long DIY for an S class, but same basic engine and definitely worth the read. Explains how to take fuel line off and the Pelican DIY just glosses over this step. You'll need a small cup of sorts to hold under connector to catch the fuel as there is a fair amount stored in the rail. Also, do this step first while the valve covers are still on so you don't get fuel in the engine.
http://www.benzworld.org/forums/w220...r-sealant.html

Removing MAF:
http://www.pelicanparts.com/techarti...eplacement.htm

Valve cover gasket DIY:
http://www.pelicanparts.com/techarti...eplacement.htm

Also... if you do this, go ahead and order another MAF bracket. 112-141-04-40
They are plastic and can be quiet brittle after 13 years in the heat of the engine bay. Don't ask me how I know.

quip11

Ditto with RCP.

I just finished all that was mentioned: replaced valve cover gaskets, breather cover seals, breather hoses (4) and plugs (12). I noticed oil on some of the plugs after I took them off. I cleaned all the coils and plug boots, cleaned the breather and valve covers. I waited 24 hours for the RTV seal to cure before restarting. No more hesitation on acceleration, no more rough idling, and stalling when coming to a stop.

All your symptoms I had experienced. I used to wait 5-10 minutes after starting the car before I drove off. When the car is warmed up, the hesitation was not as rough as it was after the initial startup. Hope that helps.

Davis_C320

Would you mind sending me a parts list on parts I need to buy? Gonna tackle this next week hopefully. I've cleaned the MAF before but the hoses look brittle and I can see oil spot around the gasket...thanks for all the info and help!

quip11

1121590080 Air Boot Seal Ring To MAF
1121590180 Air Intake To Throttle Body
1120180182 breather hose
1120180282 breather hose
1120180382 breather hose
1120180682 breather hose
1179901578 hose connector
1120160221 (L) valve cover gasket
1120160321 (R) valve cover gasket
0280217515 MAF sensor

I've added the other parts I replaced just in case you decide to do and you don't have the part numbers. Good luck.

RCPDesigns

The links with 'Pelican' in them have a 'order parts' button in the middle of the page.
quip11's list looks correct though I don't think you need the MAF sensor... though you might. One way of testing the MAF sensor is to unplug it and start the car. The ECU will use a default mapping that should be fine. Would be a quick test to see if the rough idle goes away.

BTW, here are a few tips. Since you're a DIYer I'm sure you are familiar with these but doesn't hurt to throw them out there.

1) Get a real inch-pound torque wrench. I bought mine from CDI off Amazon. I paid $130 or so. The valve cover bolts are about 70 inch-pounds and I was pretty surprised to see how little effort that is. You can pay less for a torque wrench but IMHO, going cheap on a precision instrument defeats the purpose. CDI only makes torque wrenches and Snapon resells them which speaks volumes for the quality. My other torque wrenches didn't have the accuracy at such a low setting.

2) You probably already know this, but the hood support (driver's side) has a red button. Push that in and you can extend the hood further up until it is almost vertical.

3) I never found the torque specs for the fuel line on the rail. The long link I posted suggested making a mark on the nut and the rail such that you can tighten the nut back like it was. I guess that works. Have a plastic cup under it when you take it off and do that first before the valve cover gaskets come off.

4) Lay a rag over the exhaust manifold/pipes. If your gasket has been leaking the back couple of bolts come out with oil dripping down. Really not much elsewhere but handy to have the rag down.

5) The smaller hose on the right (driver's) side connects to another hose that connects to yet another crazy contraption in the center next to the MAF. The connection part is hard to see and easy to break. Cut the hoses off (that goes for all of them). Just don't cut too far into the hose and damage the *plastic* connector. Way too much plastic.

6) You really need the special 17mm bent open ended wrench to get the spark plug boots off. I think you could do the job without taking them off and just laying the coils down but there isn't much room. The tool is only $17 or so and very much worth it.

7) Obviously if the spark plugs are close to being ready for a change... now would be the perfect time.

8) NO SEALANT on the gasket. The sealant is only for the smaller breather thingy (official name).

9) That little plastic cup full of gas from when you removed the fuel line is a perfect place to stash those nasty bolts you remove. By the time you put them back on they'll be nice and clean.

10) Take your phone and make a video of the engine once you remove the air cleaner. Just do a slow pan from the front right, down the coils, around the MAF and over to the left side and back up to the front. This saved my butt because there were two things that I forgot how they went back on. All I had to do was review the video. Those two things were the coils and the big breather hose. While you can have the coils in any order, mine had shorter and longer wires and as such, the coil at the front and the coil at the back were really not interchangeable. The big breather hose (right side, goes to bottom of MAF) can go on either way and appear correct. One end has a sharper curve and that end goes on the valve cover. If you don't have it that way, then it doesn't clear the fuel line very well. Both of those things were obvious in the video I took. I used to take pictures but I found that I never quiet had the correct shot (because you don't really know what you're looking for when you start taking it apart). The video covers a lot.