CFH55

I posted this question in my new member intro thread, but I figured creating a new thread dedicated to the issue I am having would be more efficient. Any advice is greatly appreciated. I tried to layout as much detail as possible.

I have a question for you guys, I have searched the forum and I haven't really found any post's that describe the same thing as what is occurring in my CLS. So, basically I am getting a rough idle, prior to changing plugs I was showing a slight misfire on all cylinders which the plugs corrected. I now pretty much feel a rough idle when in park, drive and reverse, it is slightly less in neutral however this is only a barely noticeable amount. The RPM's do not fluctuate nor does the vehicle hesitate when it is revved or during normal driving operations. The rough idle feels like what it must be like to be in your 80's and have that slight shaking in your hands that comes with age. It is like a shudder, not extreme but noticeable to me as I am OCD about my car. Anyway , here is what has been done to correct it without success. Oh and this issue occurs whether the vehicle is hot or cold and likewise occurs whether the atmospheric temperature outside is warm or cold. Also turning the A/C on or off does not alter the issue.

1. replaced stock idler pulley with another stock idler pulley as I noticed a slight oscillation in it. (Not to the extent that it would cause damage, oscillation amount was within acceptable range as per MB, however I read too many horror stories and replaced it)

2. Motor mounts were replaced. (was done at dealer, amazingly covered under warranty...)

3. Replaced spark plugs. (gauged properly and torqued correctly and used OEM plugs)

4. Replaced engine intake air filters. (everything was properly resealed and seated into position)

5. Ran some fuel injector cleaner through her. (once about 3 months ago and prior 6 months ago)

6. Checked vacuum lines and found no obvious leaks, which was reaffirmed by the lack of a CEL.

What I think it may be?

1. Dirty MAF and/or throttle body?

2. Tranny mount shot?

3. O2 sensor?

4. Inadequate fuel supply due to fuel pump not operating correctly?

5. Fuel filter is dirty?

6. Other more serious things such as crank case position sensor, ECU not operating correctly, Faulty engine mounts (the ones I had put in), I am not really sure.

The idle issue is not causing any decrease in performance, the vehicle starts on the first try, I use only premium gas 93 octane, car is driven daily and is parked inside so no water from fuel or environment, Oil done every 3500 miles, recently flushed all fluids including the tranny fluid and filter. So I am really at a loss, if I could get some guidance from any of you guys who have experienced a similar issue I would appreciate it so I do not correct things which do not need to be. Thanks for the help everyone!

vvrjrlaw

Couple of things.
1. If the engine mounts were changed you should have changed the trans mount. Vibration, "stick shudder" are all the result of a bad mount and could cause issues in the power train like center support bearing wear or u joint wear.
2. How did you check to verify no vacuum leak? Would urge either a vacuum gauge or carb clean or some other hydrocarbon based solvent that will cause an increase in rpm. Spray at connection points and listen for increase in rpm. Visual isn't enough because when it visual it's happened not on the verge of happening. Remember CEL only triggers when the vacuum drop affects other engine functions but it could throw a code.
3. MAF is possible you could unplug it and check but that will trigger a code. Remove it and inspect it. Get MAF cleaner and clean it. Remember MAF CLEANER, don't want to damage the MAF. No code or CEL would suggest that it is currently in spec.
3. Throttle body should have no real impact unless it is that blocked that it restricts intake air and that would trigger a code.
4. O2 sensor would trigger a CEL and the idle would be rough and performance would suffer.
5. Inadequate fuel supply whether caused by inadequate pump pressure of dirty filter may be an issue but that would cause a lean condition at higher speed with misfire and CEL. You can check the pressure by monitoring same at the fuel rail feeding the injectors.
6. Crank position sensor is either working or you are dead in the water. They get warm and as they approach failure they shut down the engine until they cool off. If it hasn't shut off its still good. They also throw a code.
7. ECU not working properly. That is THE unit that operates the car. Anything wrong will trigger a code and possibly CEL and it's not going to start up first time with nothing more than a possible shudder.
8. Motor mounts. If you believe them to be defective take it back to the dealer and tell them as well that the trans mount needs changing.
I don't believe that you have a serious problem but if you're like me it's bothersome. My first guess AFTER YOU CHECK FOR CODES is the transmission mount. Good luck.

ItalianJoe1

I would say possibly the trans mount first, as above it should have been done when the engine mounts were done.

Clean the TB, they do tend to get sludged up pretty good with PCV residue and it causes the car to have to run a different idle throttle percentage to still hit the airflow targets, this can cause a slightly uneven idle even though everything is technically in spec and not setting any codes. You'll probably be surprised how dirty the TB bore is.

How many miles on the car?

CFH55

Car has 53,000 miles on it. I will clean the TB and have the trans mount done next week. thanks for the advice, I will report back hopefully with a successful fix!

CFH55

VVRJRLAW, to inspect the vacuum lines I first visually inspected them, and then as you suggested sucked a slight amount of Mobil fuel injector cleaner through them and did not see any noticeable increase RPM. I agree, that this issue is not a major problem. However much like you it is bothersome to me. I think what you guys have suggested in respect to it being a trans mount is the most likely and logical culprit. When I have this replaced I will report back whether the issue has been fixed. I am going to clean the TB sometime next week as well so fingers crossed this will alleviate the "stick shudder" in my car. Thank you guys for the advice I really appreciate it!!!

CFH55

Hey everyone, just wanted to give an update on the rough idle issue I have been encountering in my CLS 55. I cleaned the throttle body and also the MAF, with no change in the rough idle issue. The car goes up Monday of next week to the dealer to get looked over, (I use the dealer since I have a warranty and we are personal friends with the owner so we do not get shafted), I will report back with what they find and ultimately what corrected the rough idle. Have a great weekend!

vvrjrlaw

Make sure he scans the vehicle and gives you the codes to post here.

CFH55

I will post any codes that show up and also all other information regarding the cause and the ultimate fix. I appreciate the help from you guys and I hope that what I post regarding the cause and ultimate fix can be useful to others! I will keep you all informed with what is up.

CFH55

As promised I wanted to let everyone know what was found to be the cause of my rough idle. I spoke with the tech at the dealer and he informed that there were no DTC codes present upon scanning. As was suggested and what I assumed to be the culprit after doing more research the trans mount was collapsed and after being replaced the car is perfect now, not even the slightest shudder. Now the other things they are doing all of which, except for my F and R brake pads and rotors, are covered by my warranty. I was in a bit of rush today when I swung past the dealer to see if I felt any of the vibration I did prior to the trans mount being replace and I will post a complete list of everything which was done when I pick up the car next week. I am also getting near time to get some new tires, I want something that is grippy, I do not need all season as we rarely get snow or ice here, and has a somewhat good tread life and is mid price range cause these cars simply eat tires and i cannot justify spending $350-400 a tire... What have you guys had good experiences with? On my old C55 I used to love the bf goodrich G-force T/A KDW tires but they do not seem to be made in our size. Anyone recommend something similar?

thanks for all the help!

vvrjrlaw

What I have found after having several sets of rear tires "eaten" is that when the car is in "down" mode the car has serious toe out thereby wearing the insides of the tires. When it is raised the alignment is perfect. My Indie showed me the situation with the car raised and lowered on his alignment machine. Since Mercedes lets the vehicle drop automatically but doesn't raise it automatically you must raise it manually or you will wear out the tires prematurely. I make a conscious effort to manually raise the vehicle after a run to keep the tires as long as possible. So far so good and I am using the Bridgestone Potenza tires made for the vehicle. Very expensive but the car sticks to the roadway like glue.

CFH55

vvrjrlaw, are referring to the lowering action that occurs when the car is driven I think its something like 70 MPH? I assumed that the slight lowering at higher cruising speeds would revert back to the normal vehicle drive height once you decelerated below a certain value for a set period of time? As for manually raising the vehicle using the airmatic system, isn't this action only permissible up to a certain speed? I understand what you are getting at, however it doesn't seem that driving with the vehicle in a raised configuration at all times is the best in my mind. I understand the values of height difference may be presented as somewhat nominal in the manual and appear as such in real life, however based off of the drive dynamics of the vehicle and the location of it's CG, I am not sure if the increased loads imposed by this will not ultimately result in premature component failure and also noticeably reduced handling, performance, aerodynamic efficiency, and resultant increased fuel consumption. I get even wear on all my tires and I am not sure that what you are experiencing is normal? I may be wrong, so please correct me if I am. BTW I order Bridgestone Potenza S-04 Pole Position tires.

Thanks for everything!

vvrjrlaw

You misunderstood. The vehicle "lowers" in self after 70mph. But it does not return to the original position when you drop below 70. When my vehicle is raised there is approximately three fingers (4 inches give or take) between the tire and the fender. That said I have no problem with the vehicle lowering at 70 and above but when that happens there is significant toe out hence the handling characteristics and sticking like glue to the roadway. But at lower speed you don't need the "squatting" and the continued down condition causes wear on the inside of the tires at a substantial rate. Understand the tires are "gummy" to begin with and wear during the course of normal driving. I have seen tire "spray" on the side of my auto. Since I have taken the time to check the vehicle position ( just look at the body raise switch, if it's not lit you're down) and make sure it's up the tires wear fine. It will go down on its own when you exceed 70 so no worries but when you are going slower the car handles fine in the up position and if you're over 70 you can't raise the vehicle manually. Also keep track of tire pressure because the sensor system monitoring pressure is not always accurate.

CFH55

Please do not take this as me trying to be a "wise-a**" or argue with you about what you said, however in the owners manual I believe that what it says regarding how the ADS and vehicle height control system operate contradicts what you just posted.

Here is the quote from page 239 of the owners manual.

"Vehicle level control
Your vehicle automatically adjusts its ride
height to
increase vehicle safety
reduce fuel consumption
The following vehicle chassis ride heights
can be selected:
Normal
Raised
The vehicle chassis ride height is raised or
lowered according to the selected level
setting and to the vehicle speed:
At a speed exceeding approximately
68 mph (110 km/h) with normal level
set or exceeding 75 mph (120 km/h)
with raised level set, the ride height is
reduced automatically. The table on
the next page provides an overview of
the vehicle levels.
With decreasing speed, the ride height
is again raised to the normal level."

The actual values as per the manual page 241 as to the amount of ride height increase or decrease are as follows.

"Vehicle level
when stationary
Indicator lamp
( page 241)
Suspension
tuning
Use for Ride height increase
over normal
Automatic lowering
Normal Lamp off Comfort For driving on normal
roads
None Max. approx. 0.4 in (10 mm)
Normal Lamp off Sport 1 or 2 For driving on normal
roads
None Max. approx. 0.6 in (15 mm)
Raised Lamp on Comfort For driving on rough
roads or with snow
chains
Approx. 0.8 in (20 mm) Max. approx. 1.2 in (30 mm)
Raised Lamp on Sport 1 or 2 For driving on rough
roads or with snow
chains
Approx. 0.8 in (20 mm) Max. approx. 1.4 in (35 mm)"

also on page 241

"At a speed of approximately above
75 mph (120 km/h) or if the speed
amounts to between 50 mph
(80 km/h) and 75 mph (120 km/h)
for approximately five minutes, the setting
raised is canceled. The indicator
lamp
2 in the button goes out.
If you do not drive in this speed range,
the raised level remains stored even if
the SmartKey is removed from the
starter switch."

So as far as I seem to interpret this, it appears that the vehicle will lower however once operation returns to a certain speed value for a set time frame, the vehicle will return to normal operational height. So the increased squatting should be reduced. I think you are trying to say that once you drive at 70 the car will lower and even if you reduce your speed to within the parameters stated in the manual for the required time frame, the vehicle will continue to stay at the reduced level that occurs at higher speeds. This is incorrect, the vehicle will raise back up as is stated in the above quotations from the manual. I do understand that these tires are gummy and I to be honest I am not really upset with the tread life, I think 30-35k miles for a set is perfectly acceptable given the nature of how our cars drive and their weight. I really just wanted to hear some members opinions on different tires they had tried so I had a few first hand accounts as to how they performed. Anyway please do not take this as argumentative, I really do appreciate the advice given on this forum. I just wanted to explain where my info was coming from.

Thanks for everything!

vvrjrlaw

Well I will accept the information provided by the latest laser tracked computer alignment instruments over the manual when it comes to alignment and how the vehicle operates. Besides my own operation of the vehicle validates the premise of the computer alignment instruments. No offense taken but I do it because I have the empirical data, it works and my Potenzas are 3 years old with no inside wear. Good luck.

CFH55

I completely agree with you, it is your vehicle and if you find that it performs best operating in a specific manner then keep doing it. I have even wear on all my tires and she tracks straight and true. I just wanted to post what the manual states in case any new people were to read this thread.

vvrjrlaw

Thanks for the response. It is almost auto specific but given the notariety of being a "tire eater" I just wanted to post a logical reason for this notariety and a possible solution based on information my trusted inde provided to me. Good Luck