Hey all,

I'm hoping others can give me some ideas to throw at dealership who claims to be unable to reproduce a problem I'm having with my C350 I just bought a couple months ago.

Shortly after getting it, I noticed that the car sometimes "stutters" forward when letting go of gas pedal at a dead stop. It seems to happen more when the car was driven aggressive recently or when it's very hot outside. If I high rev the vehicle in nuetral for a few seconds, then put it into gear when rpms settle, I can sometime reproduce the stuttering forward creep.

I've also noticed the engine(?) sometimes shaking during a cold start while in neutral. A few times I've heard a fast "flub, flub, flub, flub, flub, flub, flub" near the hood right after cranking (about 1/8 sec intervals, about 8 flubs).

At it's worst, the car shaking is felt in my shoulders and hips while in neutral. The stuttering forward can also be bad and felt at 1/8 intervals. It was bad enough one time that a date of mine asked "whats wrong with your car" when creeping forward after a stop light.

Once I depress the gas pedal a little, everything seems ok, though I do feel the performance is under par. I just "upgraded" from a 2006 C350 (which I still have) and it feels more powerful and faster 0-60. Also, the 2006 C350 easily get 24mpg with conservative driving on my commute to work. The 2008 gets 18/19. On freeways, the 2006 can easily hit 29-31mpg, but the 2008 is struggling to get 24/25.

The 2008 is a certified used car, so it should of been "refurbished" I believe. The dealer checked all engine and tranny mounts without finding any issues. They mentioned it might be a torque converter issue, but I notice the shaking in idle. I've noticed in drive at a stop, the RPMs are just under 500rpm, which seems low. However, the dealer said they did a full computer diagnostic and all performance specs are within their normal thresholds. There is not a check engine light. They said that perhaps a fuel injector cleansing would help.

The frustrating part is that all of this doesn't happen all the time, it really seems to be dependent on engine and air temp. All I know is this car is not performing nearly as well as my older 2006 C350 which has almost twice the miles (80k). Is it possible the last owner messed with the computer? Would MBZ be able to tell? Any other ideas?

-Joel

 

maybe the housing over the engine is loose or broken?

 

I don't have an answer to your question but my 2010 sometimes does that stutter forward thing once in a blue..it will just kind of jerk forward for a split second when I let go of the brake at a light then its fine..I hadn't given it much thought until you posted this..hopefully someone has the answer..N

 

If MB dealer isnt going to stand behind the performance of a CPO, the return it. Just the huge difference in MPG means something really not right with the 350 engine. The dealer should run the full diagnostics while you observe and prove there are no error codes. Make sure the TCU has had the latest transmission software update.

Could even be the engine mounts. My W204 is so quiet when I start it cold that I make it a habit to look twice at the tach to make sure the engine is actually idling.

 

Thanks for the response so far guys.

I'm curious if you could tell me what your MPG is for your W204 (Only if you have C350 as it has a different engine as I understand it). And that would be MPG in normal driving city and highway (city, no timing lights or feathering, just normal stop and go) (highway, 70mphish).

They did check mounts, all looked ok

 

Nothing wrong with your MPG, these numbers are the norm. My car is '08 C350 with 30+k miles on it, averages a tad below 20mpg since I bought it (mixed driving, mostly city). I've seen highway mpg get up to 27-28 at the most (however, I have rarely taken it on a long highway drive). In the city it averages ~19mpg.

 

My fiancee's 2006 C230 Sport had the same perceived shaking at cold start. Dealer advised that the car runs rich intentionally at cold start.

Makes sense are we can run rich all day long but we can only run lean once.

 

I have the 350 and I average about 23.8 mpg - I just reset it for a trip to visit my son at Penn State and after 400 miles of hwy driving (80-100mph hwy driving) I averaged 27.8 miles per gallon, so I think you have a little something worng. (BTW, also a 2008 car, 28K miles.)

I also get a little flub flub at cold start, I described it to the dealer as almost a diesel sound, he confirmed it is normal - cannot remember the exact explanation, but will try to look it up and get back to you.

 

I should have added above - there is no shaking as you describe during start up, nor is there any creeping forward at any time.

 

Mass Air Sensor on way out ?

 

To the OP, take your car back to the dealership and ask/demand that they perform a full diagnostic on the car with their computers... Could be many things but something ain't right and it sounds like a computer/timing issue, may just need a ECU reprogram.

Are you getting gas at the same place every time? You may be getting bad gas or gas that your car doesn't "like". Try another gas station. I doubt this is the problem since that wouldn't cause such poor gas mileage and the other problems.

My 2008 C350 averages 23.7 mpg over the life of the car and I've got up to 29.9 mpg on a long freeway trip. City driving is generally poor around 18/19 mpg. One quirk that I've noticed with my 350 is that outside temp/weather play a huge role in my fuel efficiency...temps above 60 deg. I get very good mileage and it is very poor and progressively worse below 60 deg. and below. I've never had another car that was so variable depending on the temp., kind of weird.

 

OK, I just went out to lunch and thought I would take a couple pics for reference.

* Idle is around 800rpms - (it is warm out today and I only sat there for a couple minutes, not sure if it drops after further warm up)
* Mileage just to work this morning, 34 miles one way mixed hwy/city - 23.7 mpg
* Mileage since last reset which includes the 400 mile hwy trip mentioned above, with a couple of weekends mixed in with spirited driving - 1,195 total miles - 25.6 mpg

I agree with the group, take it back to the dealer, especially since it is certified, and have them complete a full diag...Good Luck!

 

Have gotten 27+ MPG driving at high speeds through the mountains, BUT on the long upgrades one has to keep the engine below 3000 RPM, keeping the C300 in 6th or 7th and letting the torque do the work. (Obviously at a speed loss, in 7th 3000 RPM means 105 MPH and in 6th that's 94 MPH). Once you get into 5th or 4th, the MPG deteriorates drastically.

Around town it's 20 MPG. Only times it gets down to 18 MPG is doing the insane 70 mile dash from the Pacific coast to the state capital going over the Continental Divide in the Sierra Madres at 10,000 feet, at high speed.

Seems that ordendelfai's C350 has about a 10% to 20% deficiency in MPG compared to his 2006 C350, and also most of the posters to this thread. Still recommend witnessing the error codes live on the Star. Sounds like one cylinder has a bad plug or injector (IMO).

 

Just wanted to post an update on this. All computer diagnostics came back fine, however, the dealer did the right thing and brought the foreman into it. He kept the car a couple weeks and did several mechanical diagnostics (compression, etc), and found that there was the slightest issue detected. They were surprised I noticed it given the computers couldn't. Anyhow, I guess I'm more picky/sensitive to performance than an average customer. The foreman manually inspected the pistons, found a little excessive carbon buildup and a slightly mis-seated piston (I think I am quoting this right, would have to double check paperwork). They agreed to replace/refurbish headers/pistons. The car is now silky smooth! :-D
Oh, and mpg is definitely better now, same as Acapulco Bill or better (still testing).

A big thank you to everyone's posts, they motivated me to keep working on it!

 

Im glad it worked out for you. great job pushing for your $$ spent. I will say this, there is no "refurbishing" on CPO. they choose cars w the correct miles and above average condition usually with a documented service history, usually NOT lease turnins. They are usually owned cars traded in, the lease turn ins go back to MBUSA and then get distributed. They basiclaly check the car w STAR for codes or errors, and do a visual on all the usual 100 or so things being tires, brakes, fluids, interior/exterior, and then detail and for sale. The car could have been a fluke or not maintained w premium fuel, driven hard, etc., you will never know. Thank god they found it and warrantied it so now your covered. again good job, I love hearing customers winning against the stealership.......

 

i dont have the same issue as the OP but im wondering if anyone knows.
my idle is at 500 and leaps up to 800 every other stop light...any ideas?