suzgrrl

I have a 2011 C300 4-Matic sport (automatic trans) with 92K miles that has been having a couple of strange issues that may or may not be related to one another. The first one emerged a few months ago. When I first start the car, there is a rumble and a shaking that goes on until it evens out and idles down. Seems to be coming from underneath around the muffler area, anyway. No error messages come up on the dash. It doesn't seem like a miss because it runs just fine once it's warmed up. I really haven't had the time or money to take it in to have it checked, and it doesn't seem to interfere with its performance. My thought was maybe a broken motor mount, or a loose muffler or something to do with the exhaust system.
The second issue emerged today, and is much more disturbing. I drove about 12 miles to a store I wanted to go to. Got out, spent about a half hour there, got back in to drive to my next stop, but when I went to accelerate, the car refused to shift and lost power. At the same time the stability control light flashed on (but did not stay on). When I backed off the accelerator, no issues. This kept going on each time I tried to accelerate. I immediately turned off onto a side street just in case something went terribly wrong. No error messages came up on the dash, other than the ESC light flashing on with acceleration. It finally stopped doing that and allowed me to gradually accelerate. I got where I was going, went in and got what I needed (maybe another 20 minutes), came back out and started the car. No real issues, except it still felt lurchy when shifting. It didn't cut out speed again, and the ESC light didn't come back on, but I made sure to accelerate VERY gradually to be safe. For the rest of the trip, the car occasionally lurched on deceleration and at cruising speed when I took my foot off the gas, but no more ESC light. The problem did not occur at higher speeds, only lower ones. I have not yet checked the tranny fluid level, although I'm getting ready to do that now. I figured I'd get an error message if the fluid level was too low, but maybe I shouldn't assume that. Any ideas what could be the problem before I have to bend over for the dealer? I'm a woman on my own with very limited knowledge about cars and don't want to be taken advantage of.

suzgrrl

Aaaaand now that I've checked around I learned that there's no way to check the fluid without removing the engine cover, but also that it's unlikely to be a fluid level problem unless there's signs of a leak. Which there aren't. So...maybe a sensor failing?

superangrypenguin

You can't check the tranny fluid level unless you have a model where there is a dipstick tube and you buy the dipstick tool itself which does not come with the car.

On models like mine that dipstick tube isn't even available!

Irfie

Okay, I can speak about the 2nd issue and let me explain it in good terms so that you can understand it clearly without using terms which you might not.

You are having less power is probably because your car is not wanting to shift (change gears), this could be because the transmission oil might be low, there is no way to check the transmission fluid as there is no dipstick or any gauge to check that, you can however buy the dipstick and follow a few methods to check the transmission fluid.

However, you can also buy about a litre of oil and ask any of the garages to fill the oil (usually from below) and then you can drive your car around. If you have no issues then youre good, if the issue again comes up then come back here and id guide you on step 2.

good luck!

suzgrrl

Thanks for responding. My problem is, I've read it's not good to overfill the transmission fluid (as with any fluid) or it will cause damage. So I don't think I want them to just add fluid without checking. Will they be able to do that?

suzgrrl

Can an oil-change place check the fluid level?

Demvang

Have you tried TRANSMISSION RESET?

suzgrrl

No, I didn't know about it. I will try it and see what happens, thanks! Might have been needing this for a while, since I've been noticing a bit of lurchiness when changing speeds or decelerating for a while, but only occasionally. I hope this will fix it!

suzgrrl

OK, I did the reset and it seems to be better so far.

suzgrrl

I still have issues with rumbling and shaking when I first start it though. It evens out when the car idles down and warms up. But it seems like it's starting to be present even when I'm driving now. Normally I have music on and don't really hear it, but I made it a point to have everything off when I drove it today and it seemed like I could still hear it. So I'm wondering about the following possibilities: Bad motor mount; exhaust issue of some kind, like a hole in the muffler, or a catalytic converter issue; or something being out of balance. I just don't know, and it's hard to describe. But it's not normal. I don't smell anything sulphur-y like from the cat converter, but it has happened briefly once or twice. (Doesn't every car "fart" sometimes? Mine all have at some point, lol!) Any thoughts on what could be causing the rumble and shake?

Irfie

I don't think it's a mount issue, because if it is a mount issue then it would be present all the time and not at times.

The problem could be as you described because of the converter

Do you have this issue when you are idle?
Do you have it on high rpms?
Try putting your car on N and give throttle to see if it makes the sound
Do you have shift problems?

I assume your car hasn't yet thrown an error or check engine engine yet.

suzgrrl

The rumble and shake is most pronounced at idle, especially when just starting up. Not sure what RPMs are normal at idle or regular drive; it's an automatic, so I didn't think I could really change that. If I rev it up it will do it as the throttle comes back down. I do have shifting problems. It's not shifting as smoothly anymore, even after doing the reset. Yesterday evening I took it up a winding hill and it kept shifting up and down a lot each time I changed speed for a curve, etc. There is no error or check engine light. Honestly, it's been going on so long it's probably there to a lesser degree all the time but I've gotten used to it and don't pay attention to it anymore except when it starts. The bigger concern for me is with the transmission shifting issues. Because it sounds like it's a pretty expensive problem regardless of what it is.

Irfie

So there could be 2 things out here -

Your car is shaking when idle but as soon as you pump gas the shaking goes away, this means that you car isnt getting enough fuel to keep the engine running smoothly or else it wouldnt shake when idle. You can use the fuel cleaner (Part Number # A 000 989 25 45 12) to put it in the fuel tank and it would clean your injectors. That is something cheap to get and a good fuel addictive for Mercedes.

Now regarding your shifting issue -
The transmission could be acting up because you never changed the transmission fluid on your car, the most easy and cheapest solution at this moment would be to change your transmission fluid with the transmission fluid filter.


Transmission fluid required - (From 5-8 Litres, each litre would cost around USD 13)
Transmission Filter required - 1 (USD 35-40)
Labor required - Around 30-40 mins max (not sure whats the rate of labor at your end but i paid like USD50 to the mechanic)

That would be your first point to look at. If this does not fixes the problem then my mind would go to transmission converter

Let me know how it goes.

Irfie

Did you manage to sort out this issue?