FIREfreezerC250

Hi everyone. I have asked about this issue before, but I thought I'd make another post with the correct title this time, in hopes that somebody might finally be able to give me a definitive answer.

I'll keep this as short as I can. I bought the car last December, it has had a rough idle ever since I bought it. I got the transmission valve body replaced by MB, and the engine valve cover replaced by a MB private shop. Neither "fix" has resolved the issue.

When I start the car it revs at about 1200 RPM for about 20 seconds like most cars do, and then decreases to around 800 RPM and starts bogging and shaking, RPM all over the place between 700 RPM and 1000 RPM. It does this for about 2 minutes, or until the engine reaches 73 degrees Celsius, and then starts idling perfectly. You can literally feel it, like it moves from open-loop to closed-loop at that point (just my untrained guess), you can feel the transition. And then the car idles and drives perfectly fine.

The codes that have accompanied this issue (and are currently active) are as follow:
-P0172: Cylinder Bank 1 too Rich
-P0171: Cylinder Bank 1 too Lean
-P0068: MAP/MAF Throttle Position Coorelation
-P0106: MAP Pressure Circuit Range/Performance Problem

Sometimes it's only a few of these, sometimes all of them are active.

Can anybody diagnose my car? I'll pay a $60 bounty to anybody who can correctly diagnose my car.

I will be taking it into iAutohaus as soon as I can for them to diagnose and resolve the issue. I'm so ready for the CEL to be off.

TimC300

Im not too familiar with the C250 engine but to me it sounds like a leak of some kind, then fixes itself(idles normal) when intake pressure is built up. I would check all vacuum lines, seals, hoses etc leading to the throttle body. Inspect the throttle body and clean it if needed. I've searched around a bit for the P0068 code and some have luck with it being a faulty seal, another said a vacuum line? was unplugged, seems they forgot to hook it back up after changing the air filter. not sure which one they are talking about though. Ill see if I come across anything else to check in the mean time.

JettaRed

iTrader: (1)

It could be a bad secondary air pump that runs (or not) at startup; a bad/dirty throttle body; clogged fuel filter; bad O2 (A/F) sensor (pre-cat); a bad/dirty MAF; or a vacuum leak that closes once the engine gets hot.

Why were the transmission valve body and valve cover replaced?

When were the spark plugs last changed? Fuel filter? Has a smoke test been done to find any vacuum leaks? How many miles on the car?

FIREfreezerC250

@JettaRed The transmission valve body was replaced because of a separate issue the car had when I bought it. The engine valve cover was replaced because it was determined by iAutohaus that there was a minor leak which they claimed was causing the shaking/bogging issue.

Most of the stuff you mentioned has already been checked, a few of them haven't however (or at least weren't relayed to me by the mechanic during it's last visit).

@TimC300 I will mention the possibility of it being a hose leak when I take it in for diagnosis again. Hopefully they can give me some kind of discount considering that the valve cover replacement that they did was supposed to fix the issue (it did run much smoother with the new valve cover installed).

It's going to be about 2 weeks before I go back to the mechanic, but I will update this post with their new diagnosis.

JettaRed

iTrader: (1)

Have you heard of smoke testing? You can get a smoke generator (burns mineral oil) and an air compressor and connect it to the intake with the motor off. The idea is that any leak will appear as smoke vapor in the engine compartment. Is that how they found the leaking valve cover gasket or did they just see oil on the head?

FIREfreezerC250

Just wanted to give a quick update. So I took my car back to iAUTOHAUS for diagnosis. Apparently they came to the conclusion that the part of the wiring harness that delivers power and information to the throttle control system is faulty. They quoted me $750 to repair that part of the wiring harness. They're saying that this is the reason my car is idling rough and has various throttle system and MAF errors/DTC's. Apparently the repair should be done by Friday afternoon. I'll let you all know the results when the time comes.

FIREfreezerC250

Ugh. So they aren't done with the car (like I knew they wouldn't be). They said they are in the middle of testing every wire that goes from the ECM to the throttle system. He said they're trying to make sure they don't "have to replace the whole wiring harness".... This is so insane. How can this be such a big problem? I can't even imagine how much money it would be to replace the entire wiring harness... They never outright said it would come to that, but based on my past experience anything is possible. This is just insane...

TimC300

Im curious how the harness is "faulty". Tell them to save all the parts so you can look at them.

CaliBenzDriver

As others pointed out his really sound like a basic unmetered air leak. *NOT* a failed throttle body, harness.

Call the stop for the "whole $10k harness" scam job. The ppl working your wallet are now calling big tickets to meet bonus... nothing to do with your engine issue.

How long as your engine done the funny cold idling? Any chance this is related to "new valve-cover job" and leaky hard seals being reused?

An honest mechanic should diagnose your engine :

• listen for pressure/vacuum leaks
• spray brake cleaner around L4 head: injector seals?
• Fuel trims idle numbers
• Fuel pressure

It's a minor issue that closed-loop is able to iron out but still calls all the faults about it. Don't hurt your engine ignoring that.

I am going to bet it's an air leak so ECU puts out more fuel to deal with a lean engine mixture. So your trims are like +15...

It's nothing throttle body related because of the gamut of active codes. If it was TB, the ECU would only flag mismatch values period.

That shop has PROVEN TO BE THE WRONG PLACE to deal with your business...

FIREfreezerC250

It's been doing the funny cold-idling thing since I bought the car (yes I bought it anyway, and it has deemed to be a pretty good car, all things considered). When they replaced the engine valve cover the issue went away for a while, but then it came right back.

So I'm going to ask to see the fuel trims and have them do a smoke test like @JettaRed was saying above. I'm also going to show them your comment @CaliBenzDriver and tell them I want them to pursue your line of thinking, because I agree with what you're saying.

I'll give an update on Wednesday or Thursday.

Demvang

I would try to clean the MAF + throttle body.

JettaRed

iTrader: (1)

Be prepared for them to poo-poo anything you hear in a forum because they are, of course, the experts and been doing this longer than dirt is old.

chinatownabc

Hey,

I read through you comments and everything I have the exact same issue, so when I got the car completely find, I had the the hpfp replaced at the dealership and then the issue of the rough idle started. Like you said on cold start. I did notice after the car is warmed up the issue is gone, after the car sits for 6 to 8 hour the same issue happens. I hve change the sparks and ruled out the o2 sensors as well. I'm thinking leaky injectors causing pooling of fuel in cylinders. Strange thing is if rough I open my window or step on my brakes it sometimes makes it stop and smooth out the idle asap.

FIREfreezerC250

I'm going to keep it short and sweet. I need some advice.

I dropped my car off Tuesday the 9th at the mechanic for rough idle, MAF/Throttle Position/etc. DTC's. When I dropped it off, they quoted me $750. It's now been there for almost 2 weeks, they admitted they are in the same exact situation with the car, even after "repairing" part of the wiring harness. The car is has the same problems and the CEL is still on. I just called them and they said further diagnosis is needed which is going to mean more charges.

I feel like I shouldn't have to pay anything besides the diagnostic fee. Mind you this is the second time the car has been at this shop for this issue. The first time cost me $1000 and it didn't fix the issue. I've also spent $200 on Uber's getting to and from since my car went it.

What is fair here? I know they put man-hours into my car, but nothing has been fixed. How the hell should I have to pay anything if nothing has been fixed? And to pay even more for further diagnosis?

I asked them when is best for me to call their service manager, but I don't know what i'm going to say yet. I certainly believe I'm owed at least some kind of refund. Any advice?

JettaRed

iTrader: (1)

See my response in your other post.

Do you have your own Mercedes-specific scanner, like the LAUNCH Creader Elite BENZ 2.0? Or something just as good? If not, get one. $150 on Amazon. Then you will know for sure what your car is doing.

FIREfreezerC250

Don't you think they'd be able to tell me exactly what is going on, as I'm sure they have a Star diagnostic tool? Even if I could see exactly what is going on, I wouldn't be able to do anything about it myself. Yes I agree I should get one. But I just want this to be over. I should have never taken it in, and just dealt with the rough idle....

JettaRed

iTrader: (1)

You can't assume they have a Star Diagnostic System (SDS). They may have an Autel scanner or something from SnapOn. You say it's an independent MB shop, but what qualifications do they have? Any Mercedes-certified mechanics? What other cars do they service?

FIREfreezerC250

So I have my car back now. They had it for just about 4 weeks, attempting to diagnose the car the entire time. They replaced part of the wiring harness, tried a new throttle body, tried new intake pressure sensors, did a smoke test, analyzed and configured adaptions for hours, and probably some other things I'm missing....

And they still have no idea what the issue is. They called me up the other day and said, "You have two options, we can charge you another $400-$500 bucks for another week of diagnosing, or we can put it back together and you can come pick it up, but as of right now we don't have any idea of what it could be". So I decided to take the car back (only because Ubering to and from work everyday was draining my bank account). I asked them hypothetically if I were to continue the diagnosing process, what would they look into next, and they said something about "exhaust system" and what not.

I'm so at a loss. I, now more than ever, want to get to the bottom of this mystery. It's not even about improving drivability anymore, it's about me wanting to finally solve this puzzle. So I will say it again, there is a bounty for this solution. For anybody that can determine the cause of this issue my car is having, I will send you $120 haha. (serious though).

Once I get it paid off I'm immediately trading it in for a Benz with a warranty.

JettaRed

iTrader: (1)

I didn't see this mentioned before, but with all else having been tried, I would perform a block test to ensure there are no cracks in the head or a leaky head gasket. When the engine is cold, the metal shrinks making a break in something worse. As it warms up and squeezes everything tight, the symptoms tend to go away. Here's a picture of an Audi 1.8T head that had a crack between valve channels. Not sure how deep it ran, but it sure did cause problems until the car warmed up.



To check your head, use this.

BlackML550

Your symptoms seem to be related to cold startup when the engine is transitioning from Open loop to closed loop. Did the shop analyse your O2 sensor readings as well as the health of your catalytic converters?

Are your O2s original and how many miles? The symptoms seem to be that when in Open loop (the fuel and idle system run to a predetermined set of values) when it switches to closed loop (it starts reading actual values) - signalled by the drop in RPM - that your problem arises. Ask your shop about the O2s.

antboii

Hey Bud, sorry to hear about all the trouble you're dealing with. Did you confirm they replaced your valve cover with a brand new one? Not a used or cleaned the old one and slapped a new gasket on?

Also, ignition coils could be the culprit. (Didn't read that those were replaced)

I had the rough idle at first cold start and it smoothed out after I replaced all the sensors, intake manifold gaskets, and valve cover. This was while I was changing out the oil filter housing and gasket. (mine was leaking)

Have you ever checked the fuel pumps in the tank? They have a built in fuel filter, I've heard that can sometimes cause it. If they've never been replaced. FCP Euro sells a fuel pump kit for our cars and includes both left and right side pumps.

Shooting from the hip here as it sounds like you've had a bunch of tests and work done.

I would double check and confirm all wiring and grounds are in place and nothing got knicked or moved or was forgotten to be reconnected. With all of the (wiring harness) work they did it could be possible.

On the O2 sensor path, check those as someone had previously mentioned. Maybe your cat is clogged?? If the shop is looking towards the exhaust.

Best of luck and keep us in the loop.

Ant

chinatownabc

Any idea or suggestions. I had similar issues after the dealership changed out my HPFP. The car always started fine before this, now it seems the car is running very rich. My AFR is around 12-13. I have changed the rear fuel pumps and changed the spark plugs already. I misfire only happens when the car sits for around 8 hours when I assume is cold. I have a few people look at the car and cant figure it out. I leaning towards leaky injectors and fuel sits in the cylinder when the car is off. The misfire did go away on one cold start when the day very hot and the car was sitting in the sun all day, I assume the heat evaporated the fuel in the cylinder.

pickleboy

Hi everyone, new to the forum here
I have a facelifted W169 diesel with a stage 1 to it
I have also a problem with fluctuating RPM, it does it occasionally only on when the engine is warm. It goes from lets say 800 to 830 and back and forth
Also has another issue also ocasionally, when in highway lets say im in fourth gear and floor it the car jolts and shakes , it does the same thing also when i release the throttle, it doesnt matter if I feather the pedal or not the jolt and thud is there and also on low revs it shakes the whole car
If i shut off the engine for 5 minutes no more issue and i dont know whwn it will do it again.
I havent checked anything because its not happening every time but i have a trip planned next week and before i take it to a service center i would like any input and any suggestions so the mechanin doesnt try worthles things and rip me off

Thank in advance

JettaRed

iTrader: (1)

Scan with a Mercedes specific scanner.

JettaRed

iTrader: (1)

1. Scan for misfire codes.
2. BEFORE starting the car after overnight, remove the sparkplug for any cylinder that may have a misfire code.
3. Look inside the cylinder with a bore scope to see if there is any liquid. (You can get a cheap borescope off of Amazon.)
4. Determine if that is your problem.
5. If so, replace that injector. (Injectors ain't cheap!)