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PostPosted: Sun Jan 08, 2017 9:35 pm 
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Hi Guys

I'm trying to troubleshoot an issue on my fathers car, MB C180, 2Litre, 2001.

On start up it revs high (~2000 or more rpm) for less than a second then drops to near cutting out (~200rpm) for less than a second, then high again and low again etc....

This keeps happening until the car is driven or else until the revs are held high by holding the accelerator down for ~10seconds while stationary. On releasing the accelerator revs hold at idle as normal thereafter.

No engine light on, car drives as normal otherwise.

Anyone have any ideas?

Thanks for your help


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PostPosted: Sun Jan 08, 2017 10:05 pm 
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It sounds like a sensor has packed up. You need to read the error codes on the ECU to detect which part needs replacing. See http://www.ebay.co.uk/itm/Mercedes-Benz ... 1097686022

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PostPosted: Sun Jan 08, 2017 10:25 pm 
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Thanks DWD. I was thinking along those lines and was considering buying one of those OBDII readers. Any thoughts on the bluetooth ones available that connect to a mobile phone? loads available on amazon but not sure whether they work or not...


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PostPosted: Mon Jan 09, 2017 12:28 am 
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No sorry, I guess they are a bit of a lottery. I think the simple ones are best and a linked reader with an LCD display is probably the best option as they are older tech now and are probably more reliable. It might be worth asking a small workshop how much for a diagnosis.

Good luck

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PostPosted: Mon Jan 09, 2017 8:23 am 
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Yes the Android versions do work and work well with a mobile phone. Although I haven't seen many different version of the reader tool pass through my hands I have yet to come across anyone specifically beefing about them not doing the job.

They are also so common the prices are now ridiculously low - definitely worth having.

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PostPosted: Mon Jan 09, 2017 10:59 am 
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Sounds like a classic idle control valve fault, you need the codes read but don't be surprised if you get a lot of errors from all over the cars modules - its a MB thing

don't aim the parts cannon at it, diagnose the fault correctly

edit. CTS (coolant temperature sensor) and even a bad battery can cause your issue, clean the TB with some carb cleaner may be somewhere to start (on the car, DO NOT REMOVE the TB from the car)



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PostPosted: Mon Jan 09, 2017 12:54 pm 
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I've used them with some success, some are free to download whereas others must be paid for. I used it on an old android phone when the engine management light kept coming on the diesel Astra. They will display any readings that the ECU gets a signal for, AFM, RPM, coolant temps, fault codes etc. Because they are so cheap the cost is irrelevant, especially when you consider a lot of garages will charge £20 just to plug you in, and the money saved by not second guessing which part is causing the fault means it will pay for itself very quickly indeed.

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PostPosted: Mon Jan 09, 2017 1:08 pm 
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Thanks for the input guys, it's really appreciated.

I'll order an OBDII reader and in the meantime I'll follow flash22's suggestion and start by cleaning the throttle body.
I'm hoping either that or a faulty sensor indicated by the reader will sort the issue!


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PostPosted: Sun Jan 15, 2017 4:50 pm 
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Hi guys,

Just an update on work done to tackle this issue over the weekend.

I replaced the air filter, cleaned the MAF sensor and cleaned the throttle body. Reassembled everything and so far so good! that horrible idle surge hasn't happened since! Really delighted with the result. That said, it was always an intermittent problem, but it's looking good.

During the work I had the engine covers off and the air intake housing off. Discovered a few leaks.

As can be seen in the attached picture, I found a coolant leak at the coolant temperature sensor. I removed it, cleaned it up and reinstalled. This explains why the coolant level in the reservoir had dropped, so glad to have that addressed.

The other sensor on the front of the engine however, can anyone identify it for me? I think it must be a cam position sensor? There appears to be an oil leak from the bottom of this housing. I initially thought the oil leak, as can be seen in the picture, was coming from the valve cover itself and was preparing to redo the gasket, but on closer inspection it appears to be the sensor. Is this something that should be removed and the gasket redone?

Finally, I recorded a quick 30 second video of the engine running. https://www.youtube.com/watch?v=advQJBURBkg

For the first 10 seconds the engine is idling. A noise can be heard - almost sounds like the cams hitting off something inside the valve cover.
At around the 10 second mark however I got my helper to increase the revs slightly above idle and that noise completely disappears.
On settling back down to idle again the noise comes back. Can anyone shed any light on what that might be?

Thanks again for all your help to date.


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PostPosted: Sun Jan 15, 2017 5:21 pm 
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Is the oil running around from the cam sensor ? or is the housing leaking ? clean up the area with carb/brake cleaner it may just be the O ring that's letting past

as for the noise it may be the cam chain tensioner iirc there hydraulic on MB petrols and it takes a while for the oil to get to it, Has it got the correct oil in it ? MB is not my area tbf

edit. not sure why but MB call this sensor a 'cam magnet' and there prone to leaking


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PostPosted: Sun Jan 15, 2017 6:08 pm 
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It's the housing that's leaking by the looks of things. I might undo the three allen bolts holding it on and see if there's an o ring or a gasket that I could replace.

Yeh the oil has just been replaced. Strange because that noise is there when idling but as soon as the revs are increased it disappears and engine sounds perfect. If it's let go back to idle then the noise reappears. Strange one. From the video do you think it sounds like knocking?


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PostPosted: Sun Jan 15, 2017 6:22 pm 
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there is no seal between the head and the housing but the housing is in 2 parts what are riveted together with a seal in between (plenty of images on google)

iirc there is a MB sealant at ££ iirc if you use a non silicon based, oil proof, high temp sealant should do the trick - I would replace the part, if budget allows


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