engine stops after returning to idle from smooth start

[English Teacher]

Help! I have had my 1999 C200 for around a year now. Mostly it has run very smoothly. However, a few times over the year it hesitated on acceleration for a minute after starting, after which it would be fine.

The day after an uneventful journey of around 60 miles, the engine seemed to struggle to maintain idle speed when cold and would only rev to around 4000rpm in neutral. Idling improved after a minute or so and car could be driven but seemed to lack power.

Each time I started the engine, over a period of a few days, it would start quickly and smoothly with revs reaching around 1500. However as it returned to idle speed, the idling when cold would become rougher, with backfiring increasing. The emissions from the nearside tail pipe seemed less forceful than those of the right tailpipe. No engine management light has ever shown. (Incidentally when the ignition key is turned to where all the warning lights are illuminated, there is no engine management light illuminated – is this normal?). The plugs were checked and had a little carbon/unburned fuel on each.

A thorough check was then made for air leaks, loose wiring and blown fuses. No pressure was noticed at the fuel tank filler. I then changed the spark plugs, air and fuel filters. Good fuel pressure seems to exist on the fuel rail, as evidenced by the spurting of fuel when probing the fuel pressure release (Haven’t tried this when engine running of course).

My next area to investigate will probably be the actuator on the throttle body, but I am generally at a loss and would be most grateful for any advice.

Incidentally around the same time my brakes seemed to pulse operate with a faint shudder felt through the steering wheel, pads were changed all round but situation unchanged. Not sure if this is a related problem or whether I have been given two problems for the price of one . Neither the ABS nor ESR lights come on when driving, only before starting the engine.

I have some questions such as, should my dashboard engine management fault warning light come on with all my other warning lights, just before starting the engine?

Also, does the ECU have any internal fuse?

And almost lastly, is it better to disconnect the battery when removing sensors, so as to avoid causing fault codes in the ECU?

Finally, is there any way for the home mechanic to reset any ECU faults, without specialist equipment?

Many thanks to everyone who has read this and I am humbly grateful for any replies.

 

[English Teacher]

Updated position

Just to update everyone, in the hope that I will eventually receive some replies

My 1999 c200 stops after returning to idle from a smooth start; engine runs smoothly for around 7 seconds, but seems to stall on returning to idle.

I have now also checked all wiring and the Crank Position Sensor, which looks like new and has 13 kohm resistance.

I have thoroughly checked that the throttle body and confirmed it is opening up with the accelerator pedal and that it is return to its idle setting.

I have dismantled the MAF sensor and found it to be intact and clean (not sure what resistance it should have over which contacts?)

The Camshaft sensor seems ok also, but again this is only visual as I do not know its desired resistance value.

I have tried the engine with the brake servo and vacum hose connectors blanked off but no change.

This problem seemed to happened mainly after I disconnected and reconnected my battery.

I could really do with some help her guys, especially the following

1) Should I have an engine management light on when the ignition key is put to position 2? I have all the other instrument lights on but not this one. I have no engine management light on when engine is running either.

2) How can I test if my fuel pump is delivering sufficient quantity/pressure of fuel at the rail during engine running?

3) Could the large capacitor in the passenger footwell (which connects between terminal 30 feed and earth) be associated with my problem?

4) Can the 02 sensor or the catalitic convertor prevent engine idling?

I love this car very much and miss its smooth and calming driving experience. Please take some time to reply as I am getting desparate and don't have the means to take the car to Mercedes Garage.

Many thanks Guys

 

[BlackC55]

It need some time spent with a Star (MB diagnostic machine) to see what the cause is. First of all try leaving your ignition on for 20mins.

 

[MarkwithaMerc]

Hi
I have just finished sorting out my E240 of 2001 vintage and although i have absolutely no idea if your set-up is similar in any way to the W210, your symptoms are remarkably similar to what I bought, viz. idling poor, brakes/gearbox juddering, strange lights SOMETIMES appearing then going out again etc etc. I also had engine management light battles. The light came on several times when engine was cold and accelerating up the hill from the station! Power/revs dropped to an un-drivable low! There seems to be a 'limp-home' mode or something...
Stopping the engine and restarting it seemed to 'reset' something which enabled me to drive it home with nearly normal power but with high(er!) fuel consumption. Then the management light simply disappeared by itself-until the next time. And so on..

MAF and plug leads were diagnosed by the Gents on the forum, so i changed the plug leads for a new set and lo and behold it was like driving a new car! Nothing wrong with the MAF or anything else, I dont think.
The 10 fault codes showing at first consisted of spurious misfires, Lamda sensor failure, cat. failure etc. None of these was the real fault. My advice: Change the plugleads!! Only costs 40 quid, (for 12).
If you look on Ebay, you can get a fault code resetting tool for about 13 quid. Don't know if they work well though. My local guy has a Sykes hand-held which is definitely no Star diagnostic tool but it seems to serve for basic stuff and resetting faults.
Good luck!

 

[jibcl500]

Teacher

At a guess I would say the Air Flow Meter has failed, have you disconnected or changed the battery recently? as this can sometimes blow the air flow meter.
Simple test, unplug the meter with the engine running it should stall the engine, if it does then the meter is duff.

jib

 

[English Teacher]

Hi BlackC55

Many thanks for your reply! I agree that time spent connected to a Star diagnostic machine would be ideal, even though I have no engine management warning light lit at all, stopped or running. My reluctance to do this right now is largely financial as the car may have to be transported to the dealer. However it is also because I have reached a stubborn age, where my belief that analitical investigation of components and symptoms can bring results. Perhaps this is fuelled by the cost and number of components changed by dealers without curing problems. I will try to find time soon to replace the engine management instrument cluster warning light, as I believe it should come on at position 3 on the starter key (before cranking), but it doesn't.

I tried your first step recommendation of leaving the ignition on for 20 minutes, but sadly the symptoms remain unchanged. I will go back to basics this evening and remove the spark plugs after my engine stalls to see if they are wet or dry of fuel, then I will concentrate on the engine management/ignition components if dry. Again, many thanks1

 

[English Teacher]

Hi Mark

Many thanks for your reply. Your reply was very interesting for me, particularly your finding that the many faults indicated from your ECU proved spurious and that cheaper options exist for identifying and resetting faults. I think our symptoms are somewhat diffirent, in that my engine won't idle or keep running at all and my engine management light never comes on. However changing the plugs/coils might be very wise, especially if I see any tracking when I get to try to run the engine in the dark. What was the solution to your brakes juddering? Thanks Again

 

[English Teacher]

Hi Jib

Many thanks for your reply. Although my problem did seem to exist intermitantly before, it did largely occur immediately after disconnecting and reconnecting my battery. At this time the key was not in the ignition and the ignition circuit was off , which I thought would protect the MAF sensor. It may indeed be the MAF sensor, however I have dismantled it and found its circuits to be intact ( i.e. not blown ) and it is very clean. Ideally I would like to know the resistance for these circuits. I confess to being a little confused as some posts say that you can remove the MAF plug if you suspect it is faulty and the engine will run, whereas you suggest that if it is faulty removing its plug will stall the engine. I am thinking it can't be both. I also have the problem that my engine appears to be stalling on return to idle already, so removing the MAF plug would not result in any change. I am worried also that removing the MAF plug then running the engine will result in a fault code in the ECU. Thanks again for replying.

 

[English Teacher]

Hi Guys

Just a little update. Tried to start the engine in the dark and saw no sparking around plugs/coils etc. Inspected spark plugs after engine stalled and each had a small and equal amount of black carbon dust and the faintest wetness, perhaps suggesting I have an ignition problem not a fuelling one. I will investigate my 02 Lambda senor this weekend, hopefully, but a visit from someone who can interogate my ECU is looking more and more likely.

 

[MarkwithaMerc]

Maf Ok...!

Hi Teach
I removed the connection to the MAF on the 240 when the engine was cold and on tick-over and it didnt make any difference at all. However, i have just taken the car on a 600 mile round trip and it behaved faultlessly. So i dont think this proves anything. You may well have a faulty MAF but I would discount this at least until you can get the engine to idle first...
Dont know if this is sense but it seems logical to me..!

 

[English Teacher]

Update, so far

Hi Guys

I tried to look at my MAF sensor, accessing it from above, but unfortunately the heads of two of the four allen screws securing the exhaust manifold sheild stripped, making removal impossible for the moment. The weather and my energy level meant that acessing the sensor from under the car was not an option. So instead I tried the car with the charcoal sensor vacum supply hose blanked off, making no diffirence. In fact each time I start the engine it idles for a shorter time. I then dismantled the instrument panel, looking in vain for an engine management light. So at the moment I am no further Forward. All ideas very welcome.

I will try now to post picture of the various sensors on this forum

 

[English Teacher]

I think I have got to the stage where, in a few days time, I will disconnect my MAF sensor to see if the engine idles and doesn't just die like it is now. So, if anyone thinks this is a really bad idea for my ECU, please let me know. I still have more questions than answers on this problem I am having. Thanks Guys.

 

[English Teacher]

MAF disconnection made no diffirence

Ok ,so I disconnected my MAF sensor hoping that my engine would miraculously keep running after starting, but it continued to die on its return to idling from starting. The first time I started it, it did seem to run fractionaly longer, then it was back to stopping on return to idle. This might suggest a fueling issue, or not. I also think? heard a dull thud from around the passenger footwell/dashboard area. It didn't sound like either a stepping motor or chattering relay and i don't think it was a ventilation flap, but this is possible. I am wondering if it might be the 'big silver thing' (to give it it's technical description, ha ha) that connects between the feed from the battery and earth, that lies behind a steel cover in the passenger footwell. I think it might be a capacitor for voltage surge protection during jump starting. I will photograph it over the next few days and measure its resistance. i don't think it would be prudent to try the engine without it in place.

 

[MarkwithaMerc]

I didn't think that disconnecting the MAF actually would make any difference. Apparently the engine must be hot and the car must be driven while the MAF is disconnected to make any difference. It seems a moot point whether or not the management light will light when this is done. (see my earlier message).
If the MAF is disconnected and the car attempted to be driven, there will be no power at all but the engine will still run, albeit roughly and the car will be undriveable. At least, mine did! The engine management light didn't come on either. I dont yet know if there are any codes stored but will find out soon. Anyway, reconnecting the MAF has caused no damage and the car again drives beautifully!
As I guessed earlier, your problem sounds like it is not one of engine power management, (fuel/air ratio etc). Having said that, i dont know what it IS to do with!
Simplistically speaking, i guess if the injectors are firing, fuel pressure is OK and you have a spark, the engine should run on idle. Sounds like something is shutting-down after start-up.

 

[English Teacher]

In thread no. 11 here I stated that I could not access my MAF filter. It was ofcourse my Lambda sensor that I couldn't access. I will attempt this again this week end, weather permitting.

Thanks Mark for your replies.

 

[MB TECH WARRINGTON]

In thread no. 11 here I stated that I could not access my MAF filter. It was ofcourse my Lambda sensor that I couldn't access. I will attempt this again this week end, weather permitting.

Thanks Mark for your replies.

first and foremost, and please dont take this the wrong way,
diy repairs often cost far more time and money than getting car looked at correctly in the first place, as ive stated in many threads on here, basic repairs etc are ok, but diagnosis is something which needs looking at by someone who knows what they are doing, an expert, specialist


a quick look on our star machine in actual values can tell you if its faulty

this attitude of thinking everyone rips people off, and attempting diy in the long run will cost you needless time and money,,,, from reading all your posts i sumise that if you got it looked at correctly earlier on you would now be a happier merc owner,

i know there are many people out there who rip people off but not everyone is like that, if we as a garage mis-diagnose something (hey, we're all human) we would simply re-fit old part and not charge the customer and move onto the next possible culprit, im sure many garages on here do the same, its called gathering and looking after your customers,

if you brought your car into us, we would judging by your described symptoms
suspect a certain part, a quick 2 min road test could confirm this, then a check on star machine would really confirm/eliminate, if we were 100% sure then and only then would we charge for diagnosis,

all in your problem could be sorted in minutes,

the best advice i can give is get the car looked at by an expert. trust someone, judging by your title you are trusted to educate, let an educated technician diagnose your fault,
hope you find the cause of your problem

 

[MarkwithaMerc]

I am certain that Mr Tech of Warrington is correct as far as MB and indies are concerned and that is, clearly, the way forward. If you are like me, however, and a bit reluctant to admit defeat then i guess thats what the Forum is for; no disrespect to the Senior Members or experts intended.
Wearing my other hat as a Jaguar Enthusiast, a guy has recently contributed to his section of this months mag. with simlar symptoms with his S Type: bad idling and stalling etc. and strange fault codes. The fault was finally traced to a split vacuum hose. In fact elsewhere in this Forum someone mentions starting the engine and spraying a little Eazy-Start into the engine bay, (excluding the air-intake, i guess!), and if the engine runs better, this could be a diagnosis of a leaking hose. A similar method would be to use the plastic tube trick against your ear as a listening device. Probably safer for the weak of heart!
Just a thought anyway!

 

[English Teacher]

A chance to learn through play?

Hi Guys

Maybe this title puts an overly optimistic 'teacheresque' slant on my trying to solve my car's idling issue, however, at present I must feel that I am getting more from investigating it than handing it over to a professional. Mbtechwarrington certainly sounds like such a professional, who could be trusted to efficiently solve my little problem and if I were close geographically, I suspect it would be difficult to resist handing the car problem over too them.

My background is not in teaching, but in marine engineering, where I often found myself in the middle of some ocean, on automated diesel supertanker, attempting to diagnose some fault. Along side this, during leave I would help repair clients and my own Jaguars, Porsches and Mercedes, at my local garage. So I guess it is my love of understanding engines that drives me to investigate this fault. A career in factory process engineering followed.

Interestingly, the fault om my Mercedes changed dramatically over the weekend, with little intervention from myself. The car will now continue to idle when started from cold, albeit roughly, at around 400 rpm and with some backfiring. A few minutes later ( at about 45 degrees C )the backfire stops, as the engine revs up to 1500, then it settles back down to a normal 800rpm idle without any backfiring. As the engine continues to warm the accelerator only goes to 1500 max rpm at 65 degrees C and 2500 max rpm at 80 degrees C. However if the car is taken a run it will rev to over 5000 rpm. Acceleration seems a little sluggish and sometimes I only get to around 2500 rpm in third gear. Disconnecting the MAF didn't make any difference. I think that I can hear what sounds like air being drawn in around the front of the engine on the inlet manifold side, but this is by no means certain! Especially as I have already checked all hoses including crank case and charcoal cannister purging. I will check all routes for air ingress again thouroughly. It seems like my problem is getting better slowly by itself, but I suspect that is the optimist in me again.

 

[MarkwithaMerc]

Aha! I thought I smelled Sulzer, B&W, MDO and HFO 380! Kindred spirits I see! I am an Engineer Superintendent after some 35 years at sea as an engineer; poacher turned gamekeeper I suppose!
In situations where I am sure you have previously found yourself, you HAVE to be an optomist, especially when you have been up for 36 hours straight and still can't find out why the main engine auto slow-down keeps coming on at 60 revs! I completely understand your view-point. It is identical to my own: a little bit arrogant in that we KNOW we can sort almost anything and a reluctance to admit, (privately), that anyone can do any better. It drives my wife to drink!

 

[MB TECH WARRINGTON]

Usually When Air Mass Go, The Symptoms Tend Not Change When You Disconnect, This Is Usually Due To The Fact That The Airmass Is Doing Nothing So By Unplugging It Still Does Nothing, Just Bear This In Mind.
Id Suspect One Of 2 Things, Air Mass Or Throttle Flap,
But If It Was My Car Judging By Your Symptoms Id Almost Certainly Change The Airmass, stick with a genuine bosch/siemens one, Try It, I Think You May Like The Results,