This is a hard problem to diagnose. Check the codes. Backfires and misses cause codes to come up.

Check you secondary air pump.

 

Thanks, unfortunately i can't check the codes because euro W202s are not equiped with an OBD2 port. Im starting to think that the flexfuel conversation is interfering with things. If it was a faulty MAF or o2 sensor i would have other symptoms, am i right ?

 

Thanks, unfortunately i can't check the codes because euro W202s are not equiped with an OBD2 port. Im starting to think that the flexfuel conversation is interfering with things. If it was a faulty MAF or o2 sensor i would have other symptoms, am i right ?

Unplug the MAF and test drive it to feel how it runs.
For a faulty O2 sensor, try taking some live readings at the OBD1 port (38pin) of the STFT and LTFT and pot here.

 

Thanks guys ! I will try starting without the MAF to see if it behaves the same. I must say the car runs very well past the first 30 seconds. I will probably order the adapter too.

 

I'm back. I tried starting the car without the MAF and nothing changed. I'm really starting to think it is a fuel supply related issue. Do you know anything about the symtoms of a failing fuel pump and/or fuel pressure regulator ? I ordered a 38 pin to OBD cable and think about ordering a fuel pressure gauge as well. What kind of pressure should i expect ? i've heard things ranging from 50 to 65 psi during idle and load.

 

I'm back. I tried starting the car without the MAF and nothing changed. I'm really starting to think it is a fuel supply related issue. Do you know anything about the symtoms of a failing fuel pump and/or fuel pressure regulator ? I ordered a 38 pin to OBD cable and think about ordering a fuel pressure gauge as well. What kind of pressure should i expect ? i've heard things ranging from 50 to 65 psi during idle and load.

What scanner are you using?
Not all 38 pin adapters mated to the typical scanner will scan correctly.
And not all 38 pin adapters are created equal either.

 

I will be using a cheap bluetooth OBD2 adapter i have laying around. It is called ELM327 i think. If it does not work (my hopes are low) i will probably get my hand on something better.

 

The ELM should work o.k..

As for your issue I'm leaning towards a failing MAF sensor but obviously that's a bad guess at best.

 

I tried running the car without the MAF and it behaved the same if not worse. I will check for codes whenever i can but i'm pretty sure it has something to do with fuel supply. On E85 it requires around 5 tries (used to require 2/3 tries and then it used to run rock solid once started) and now when it finally starts it dies after a few seconds with popping noise likely in the intake. I checked with a tank of gas/petrol and it always starts right up but there's is a perceptible stumble during a few seconds which wasn't there before. I think E85 exacerbates an existing problem caused by somthing weak in the fuel supply system. I was always on the verge of not starting on E85 and maybe it's juste because of a few PSI drop for whatever reason (fuel pump, fuel pressure regularor, an injector)...

 

David,

Some more info for you to digest and check

c200 w202 runs rough when cold

hey everyone, does anyone know why my c200 would run rough when cold but great when warmed up, i recently fitted a nem lambda censor and also a new MAF censor because of real bad running probs in general whilst i was at it i put new spark plugs in aswell, any help? thanks

www.benzworld.org

 

Interesting. Do you think that it could be a clogged fuel filter, even if i changed mine like 9 months ago ? Again, hard to check without a pressure gauge but ethanol might have done more cleaning in my fuel tank and i don't have much to lose changing it again. However i dont believe i have a carbon build up problem, I dont use the car for a lot of short trips, i mainly do 300 to 500 kms of highway every week and E85 produces close to zero carbon build up.

 

Interesting. Do you think that it could be a clogged fuel filter, even if i changed mine like 9 months ago ? Again, hard to check without a pressure gauge but ethanol might have done more cleaning in my fuel and i don't have much to lose changing it again.

I doubt it's the FF, if you changed it recently. But this also depends on what gas grade you are using and the supplier (from what Ive read about other members using a subpar gas supply and lower grade can, overtime, cause issues).
Mixed opinions from members on this topic.
As for FPG, they are cheap to invest into,
or go rent A FPG at your local auto shop; and test the pressure at the rails.

Another suggestion - I give our engines some cheap TLC once a year - either seafoam top end or berryman b12 to give the pipes a good cleaning. -

 

I only use E85, i never use gas by the way.

 

Just so you know for your own knowledge.
It's your ride, so you decide.

To E85 or not to E85?

Sorry if this has already been discussed but I am trying to find some direction on whether or not to use the straight E85 in my 2008 ML350. What are advantages/disadvantages in using this fuel. Should I at least try it? Thanks.

www.benzworld.org

 

I unplugged the vacuum hose from the fuel pressure regulator and there's a strong gas smell so i think i found the culprit.

 

I replaced the leaking FPR without any improvement but it was bad anyway so i didn't bother with testing. Next thing will be checking fuel pressure, i'm thinking about the fuel pump going bad too it is starting to make a whirring noise when i turn the key.
Since the issue happens only when the car is cold (at leats 4 hours of sitting i don't think it has anything to do with something electrical like the alternator. Now i think it is either a bad fuel pump or a bad coolant temp sensor.

 

I replaced the leaking FPR without any improvement but it was bad anyway so i didn't bother with testing. Next thing will be checking fuel pressure, i'm thinking about the fuel pump going bad too it is starting to make a whirring noise when i turn the key.
Since the issue happens only when the car is cold (at leats 4 hours of sitting i don't think it has anything to do with something electrical like the alternator. Now i think it is either a bad fuel pump or a bad coolant temp sensor.

Whirring noise of the FP is normal when you turn the ignition key to position 2.
It doubt it's the FP - you said it's running fine after 30secs. You can test the FP at the rail.

To test the coolant temp sensor. Ohm it out when it's cold, use a hair dryer to it to heat it up, read the resistance again and see if it changes. When you startup the car in cold weather does the engine fan kick on at all? (Indication of not signal getting to the CTS )

 

Thanks for the reply. The reason why i mention the FP is because it did not make that noise before. I will test the sensor as you say. The fan behaves like it should, it only starts when sitting in traffic or when i turn the AC on.

 

Thanks for the reply. The reason why i mention the FP is because it did not make that noise before. I will test the sensor as you say. The fan behaves like it should, it only starts when sitting in traffic or when i turn the AC on.

On startup key to position 2, it's a simple test if the FP is priming - the whirrr noise in the lower DS back seat area. If you didnt hear it the first time, either you were not consciously listening for it, or it was wasnt priming.
Either way, this doesnt ensure the pump is producing the correct pressure to the rail. Hence, you should test the pressure at the rail to confirm.

 

It always worked but the FP noise used to be more subtle. The problem seems to be more present when the car is parked uphill and when the weather is humid. Maybe there's a valve inside the pump preventig the fuel from going back into the tank overnight and it's failed. I will check for fuel pressure asap.

 

Well, I'd still test your coolant temp sensor too.
Keep us posted on your progress.

 

Yesterday i filled half of my tank with premium gas and a bottle or injector cleaner but it made things even worse. Now the car stalls two or three times after starting.
Today i received my 38 pin to OBD2 + ELM327 adapter and tried various apps like Torque but for some reason none would recognize the car (but the connect to the adapter) I've read that this adapter can't read HFM and PMS systems but i saw vids of people do it, i dont know what to think.
Coolant temp sensor is working fine. Still waiting for my pressure gauge to arrive.

 

Yesterday i filled half of my tank with premium gas and a bottle or injector cleaner but it made things even worse. Now the car stalls two or three times after starting.
Today i received my 38 pin to OBD2 + ELM327 adapter and tried various apps like Torque but for some reason none would recognize the car (but the connect to the adapter) I've read that this adapter can't read HFM and PMS systems but i saw vids of people do it, i dont know what to think.
Coolant temp sensor is working fine. Still waiting for my pressure gauge to arrive.

re-read post #8.

As for the hi octane gas and cleaner, not necessarily made things worse. You may have had a clogged up system to begin with and this is just cleaning it up, in some degree.
If you were going to do this, I would have suggested using Seafoam or Berryman B12

 

My hopes were low concerning the 38 pin cable, it was just a 5€ thing after all.
The products you suggest are not sold here unfortunately. I think my fuel system is pretty clean to begin with. The car was really looked after and the mileage is low + one year of E85 cleaned up things even more drastically. I wanted to test an injector cleaner out of curiosity more than anything.
I don't have any symptoms of (a) bad injector(s), the car idles and runs smooth as silk when finaly started. Not a vibration and barely audible at red lights at operating temp.
However i dont know if it is me being paranoid but for the last few days i feel like there's a delay before the car accelerates when i step on it after shifting into the next gear.

 

Pump tested and it is not the issue.
The problem is getting worse and for the last few days i noticed a noise coming from the engine.
When i push the gas pedal there's some kind of random ticking noises coming from the engine, almost as if air was trapped into the injectors or something. It used to be very subtle but it is becoming more and more audible. Basically, the harder i push the pedal, like if i am going uphill, the louder the noise.

 

Pump tested and it is not the issue.
The problem is getting worse and for the last few days i noticed a noise coming from the engine.
When i push the gas pedal there's some kind of random ticking noises coming from the engine, almost as if air was trapped into the injectors or something. It used to be very subtle but it is becoming more and more audible. Basically, the harder i push the pedal, like if i am going uphill, the louder the noise.

Check the motor mounts.

 

Each cylinder has an injector which supplies fuel as commanded by engine computer, in response to calculations that depend on other sensors. So it could also be a sensor issue.

It's possible that you have a leaky injector that has pressurized fuel leak past a closed injector after the engine is stopped. This could cause an over-rich mixture when you next try to start the engine, but this is when the motor is still hot. But you have the opposite, rough idle when cold.
New or used fuel injectors are easily obtainable on fleabay.
I'd recommend you get your w202 into a shop that can scan for any codes, since you dont have a proper scanner for these older cars.

I would recommend you go back to the basics (and simple procedures first) and check ALL your vacuum lines for cracks, breaks. Also, check your cat: use the temp gun test fore and aft of the cat. Temp guns are cheap.

Lastly, your secondary air injection pump. It turns on during a cold start and runs for 60 - 90 seconds. Is this the case?
Just asking, because, you presently have no codes to tell us about and your post#1 (after reviewing your comments again)

 

Thanks, that's what i will end up doing i think. Out if curiosity, where is the secondary air pump located on my M111 engine ? I didn't even know it has one. I checked all the vacuum hoses and they were in perfect shape but maybe i could try blowing some smoke in the intake to be sure.

 

Post #3

Image I.D. & problems

Hello MB followers. I am a female newbie but have learned and fixed lots on my 97 c230 but may not always use the correct words for what Im doing. I took these pics while under my front end and Im a little concerned. Im not real sure what component this is and if its condition is bad. It sure...

www.benzworld.org

 

I checked and my car does not have a secondary air pump, they don't seem to have that in europe.

 

I'm thinking about one thing i didn't change, sparkplugs wires and boots but i have a hard time believing it would cause backfires in the intake and stalling during the high idle warm up.

 

It's possible.
That's why you need a scanner - to be able to read the codes.
You're really speculating right now w/o scan.

 

What kind of scanner should i get ? I am a bit lost. I think i will give up on this and put the car in a good mechanic's hands to diagnose this issue.

 

Autel MD802 scanner and the correct 38pin connector - DB15 38pin femaled for MBs autel ds708 md802 (do not purchase the cheap chinese garbage - they do not work)

 

I had a mechanic check the codes for me and there was no code.
I swapped the sparkplug boots with others i had laying around without improvement.
I checked for vacuum leaks with propane as well as water and found nothing. I thought i would find something because the idle doesn't fluctuate when i remove the oil cap, however the cap always "sticks" to the valve cover because of vacuum.
Sparkplugs are looking fine and they all look identical. Here's two different photos, only the light makes them look different.
However the ticking is getting worse and quite loud when i step on it and even at idle, almost like the injectors of a diesel, only it is quite intermittent. When i shut the engine down and start it again after a few minutes there's a bit of white smoke too.

 

It is definitely coming from the top of the engine and even if it was very slight for the last months it is getting louder and louder since i put the injector cleaner. I just used a screwdriver as a stethoscope and i really think the ticking i hear comes from the injectors. I remember the previous owner telling me he had the motor mounts changed not long before i bought the car and they look new.
I am noticing that the rpm drops very slowly between gears or when i put it neutral.
By the way, my Autel MD802 is on the way.