Clayton Ballas

So first I'm going to say, I love my car and got it for a GREAT price. Have had it for 4 years (approx. 60k miles) and I'm an engineer by trade so consider myself very mechanical and pretty handy. My career has been made on solving "problems".

To give as much info as possible, I'll give every detail I can.

Have had the car for about 4 years now. No warranty, no local dealer. Nearest MB is over 1 1/2 hours away. Almost exclusively highway miles, about 60 miles a day to and from work.

Work completed by myself (with help of master mechanic/friend from competing manufacturer, but very technically savvy) previously includes A/C compressor replacement, battery, alternator, radiator flush, and basic oil/air filter cleaning (installed aftermarket K&N, understand they can cause dirty MAF, but have no knowledge of them actually breaking any) at about every 5k miles.

Originally started this maint. cycle because the engine sputtered a few times and stalled ONCE at a stop light. Started right back up, no issues. Completed all "tune" up related tasks myself including engine oil. Decided it was time to change spark plugs. Replaced with iridium Bosch. Quite a pain is the buns to be honest. But was successful. While replacing plugs noticed a slight oil leak on two fouled plugs (passenger side valve cover) but not nearly enough to cause misfire.

As stated no CEL, no real huge concerns. Was fine for about 2 weeks, then noticed same slight engine sputter again at low RPMs < 2000 RPMs. Figured maybe I didn't seat plug wires or tighten down plugs properly. Rechecked torque and wire seating/config. No faults. Again, not a huge issue at first.

Fast forward a couple weeks and the occasional sputter has turned into a constant sputter during acceleration AND deceleration during any interaction with the gas pedal. No noticeable sputtering during idle. So it led me to think naturally fuel, air, spark....

Noticed a bit later as it got worse that at the lower end of the RPMs it sounds like there was a "growl" coming from the exhaust and car has slight shake. Noticeably much louder inside the car than outside the car. This sound and slight "shake" goes away quickly once you put some real pressure on the gas pedal and disappears ALMOST entirely at higher RPMs and higher speeds. I can get to coast at 60+ MPH with little to no sputter. But typical to this problem hammering down on the gas gets me to where I need to be and decreases the growl/sputter but does take quite a bit longer for power to transfer to the wheels. The sputter and growl are worse in the comfort transmission setting. Switching it to the sport mode greatly decreases the delay but does not eliminate the fault.

Figured it'd make sense to have a "real" mechanic check the exhaust for faulted/clogged/leaking exhaust, CAT, etc. Nothing found and after they checked and completed test drive they said they thought it could be tranny related (which I politely did not agree with due to sputtering happening at different RPMs and not only near shifting points).

Took vehicle to transmission shop and they said the opposite not to mention vehicle never has gone into "limp" mode or had any symptoms of tranny faults previously. They are very reputable in our town and work on both domestic and foreign. But we discussed potential for replacing valve body conductor plate, plug, etc. anyways. But did not act on any of these potential courses of action as we weren't sure it would resolve prob anyways and I have confidence I could complete that as necessary.

Back to the drawing board.

During more investigation under the hood determined I did add too much refrigerant to compressor. Fixed that. No change other than fan doesn't kick on at all times, yay one slight unrelated prob solved (as expected).

Decided to go ahead and replace valve cover gaskets, both. While doing so leaned a little too hard on what I believe is the EGR/emission shut off valve on the passenger side causing the what I can only assume is ceramic (not aluminum?) "stem" at the base of the shut off valve to snap from where it connects to the valve cover. Small hoses are still attached but there is now an audible sound due to broken part. Has not effected car negatively or positively other than a likely worsening fuel efficiency. (maybe was broken or cracked before and I just finally did it in). Replacement ordered but has not been replaced at this time.

Checked vacuum lines; no cracks, no visible/audible leaks.
Checked all connections to spark plugs. Decided to replace plug wires and hell, did the coil packs while I was at it. Sitting at 120k miles figured what'd it hurt? Did not resolve the issue.

Then unplugged MAF sensor connector and took it for a drive (under the assumption that it would work under some sort of default air/fuel mixture settings). Felt like I noticed a difference, at least at first......

Removed MAF, intake elbow and throttle body. Cleaned and re-installed. Sure I noticed a bit of a difference in performance but still growling occasionally at lower RPMs and sputter.

During driving it seems to shift and provide power at separate times causing a timing issue.

I hate electronic controlled cars. It seems like there are a million sensors that this could be. So I have ordered a new MAF.

I was told that it was likely NOT a crank position sensor because if that failed we'd be likely dealing with a car not starting or really noticeable sputtering at IDLE. which it still does not.

I did the adaptive tranny/throttle reset procedure (as per the info from this forum for the 722.6 tranny). No change.

Read online about the radiator issues. Checked and confirmed I have a Behr rad. Tranny also has plenty of fluid.

I have a instrument cluster that is getting really dim, but was concerned that maybe it was battery. Had that tested. Tested fine. Battery is less than 24 months old.

Disconnected all aftermarket electronics (I have a set of subs with 1 fared cap, 1200 watt amplifier, 2x 10 inch subs, backup camera) to ensure no extra draw on alt/battery. no change.

Even went and got a belt to bypass the AC compressor to ensure that I didn't have a DOA compressor causing issues. No change.

Fuel filter?
MAF sensor completely faulted?
Throttle body?
Fuel injectors?
Can a bad emission shut off valve cause this much engine degradation?
And all of this WITHOUT A CEL?

Really here to get ideas and more importantly how to test them. I've run out of sensible troubleshooting steps other than throwing more money at parts that I don't know will resolve the faults.

Thanks in advance.

Clayton Ballas

while driving today, really does seem like something is wrong with the timing of the fuel or air combination at low revs. definitely notice a little more as I keep driving it. such a harsh transition at low RPMs about 200-300 RPMs below transmission shifts from 1-2. very cyclic. happens pretty much at exact rpms, then after sputtering as long as i'm still maintaining gas pedal pressure, the transmission shifts as it should. maybe I didn't notice before becus everything was "normal" but this sputter seems to be much more apparent using comfort setting becus the engine starts in 2nd gear plus seems to automatically change gears at lower rpms in comfort mode making for smoother driving experience. in sport mode the rpms get higher so the sputtering seems to happen for a shorter duration and then 200 or 300 rpms later the engine shifts normally. sputtering happens even while using cruise control but not super noticeable at higher speeds. still at a loss. about to replace the MAF tonight....will update if anything changes.

Clayton Ballas

relaced MAF. MAJOR upgrade but still ocassional sputter, etc. but only drove about 10 mins. will report back once I complete the daily work grind and get about 1 1/2 hours and 100 miles on the car to see if maybe the fuel/air mix worked itself out by then or went back to normal but the throttle response and power are definitely, DEFINATELY back.

Aguydrivingacar

Hello - I'm having a very similar issue. Did you ever end up figuring out what the cause ended up being?

https://mbworld.org/forums/c-class-w...e-driving.html

slammer111

Did you check the ignition coils? Usually they throw a CEL when they go, but thought I'd throw this out there. I've had several fail over the years and the engine would sputter and do weird things at idle and below 3k. I also had stumbling issues (though it felt more like the occasional hesitation) but no CEL when stomping on the gas. It was only when the coil completely failed that the car finally threw the CEL.

If you want to test these things the cheap way, just buy and install 1 new coil on cylinder #1 then drive around for a day. If the problem is still there, install the new coil onto another cylinder and repeat until you've tried all positions. Mind you you may have more than 1 failed coil.

What's the mileage on your car? Not sure about the V6 but on the I4 they start to die at around the 200k km mark.

Aguydrivingacar

i have 200k miles on it. The guys at the repair shop when I had it there said they checked the spark plugs and packs but don’t think the issue is with that since they had spark.

slammer111

I would take a look anyways. The stumbling problems initially only occurred while I was flooring it while accelerating on a highway. The car would behave normally at highway speeds. However, the stumbling problem got progressively worse and worse over a few months. It was only after the coil completely died that the car finally threw the CEL.

Aguydrivingacar

appreciate the heads up. Do you knows if there’s a way to test the coil packs if they’re working before replacing?

slammer111

There isn't really a way. Most ignition coils start acting up under load (ie WOT) and progressively get worse until completely failing. Below a certain number of misfires (guessing it's either % of cycles or number per second) the car will not throw a CEL. That's how mine started failing. It started with an occasional stumble when I was accelerating on a highway.

The cheapest way to test this is to try a new coil in each cylinder see if the performance suddenly improves. These coils aren't that expensive either. Your mechanic's labour is going to cost more than the coils to be honest.

jggarcia.vc

I may have to do this I have a similar issue when I am stopped at a light it idles rough for a few seconds drops and than goes back. Obviously when I am driving it's fine it happens while in Drive at a stop or reverse.

denz

2002 C240
Issue:

• When the car would come to a stop the car would sputter as if it was going to die almost is if there was a vacuum leak. NO CHECK ENGINE LIGHT. The car ran great with no misfires. Only when I would come to a stop it would act up.

What I did:

• Spark plug change - didn't fix the issue
• MAF change - didn't fix the issue
• all hoses were good

THE FIX

• CPS ( crank positioning sensor )

The car didn't have any issues with starting up. I believe the CPS was on it's way to going out but not bad enough to trigger the CEL. One of the symptoms is car sputter at a stop with no CEL. Hope this helps.

Roberte01

I have a 2005 C240, 76,000 miles with a similar issue right now- Bought back in June, no maintenance history so changed fluids, brakes, and plugs. Had a no start about a month ago, changed the CPS which fixed that. Then it developed a rough idle at stop lights when the engine is warm- no CEL and codes thrown on my Xentry tool. Sometimes it's just a bit of varying idle, sometimes it'll drop to 200-300 rpm and really cough for 5 seconds or so after I'm back into the throttle, and the car won't accelerate well but then it'll 'catch' and be fine. I changed the EGR valve and cleaned the MAF with CRC MAF spray this past weekend, no change. I like the coil pack idea but likewise I don't like throwing parts at it (even though that's what I've been doing..... )