W124 running rough / rich

[ms500]

Whenever my car is idling, there is a strong smell of petrol from the exhaust and it is quite noisy (a kind of tapping / clattering noise). When driving it, it runs OK, if a little slow when pulling off. It doesn't seem to be misfiring and sounds fairly smooth when you press the accelerator, and I can't see any visible smoke from the exhaust.

Also, it takes a long time to start from warm. When cold, it will start quickly but can't hold a steady idle and the revs keep dropping, feeling like it is going to stall.

I gave it a mini-service today, including changing the air filter and spark plugs, though this doesn't seem to have made any difference. I did notice that a bit of funny-coloured oil had come through the breather hose into the air filter compartment, which was odd. I cleaned it off before putting the new filter in.

Can anyone help?

 

[grober]

Faulty/missing thermostat leading to poor warmup /cold running is one of several possibilities? Another is a faulty engine temperature sensor.

 

[Smiley]

Oil coming up through the breather probably means that there is too much pressure in the crankcases = worn bores or rings. Suggest you get a compression check that will tell you.

 

[ms500]

Thanks for the suggestions.

I just took it for a drive and it does seem a bit more powerful and smoother after changing the plugs and air filter, and the petrol smell only seems to be after a cold start, so maybe the choke is just a bit overzealous.

It is still a little noisy at idle though.

 

[Dieselman]

The funny coloured oil. Was it mayonaise coloured.? If so that is oil and water mixed either as a result of the head gasket leaking or condensation forming in the breather pipes.
Check the coolant header tank, does it have any oil or mayonaise in.?

Run the engine with the breather disconnected and see if it breathes heavily, if so have a compression test performed.

 

[Smiley]

Has the noisy idle just started or has it got gradually worse? There is a tensioner for the V belt - on the front of the engine to the left of the front of the head and on the top run of the belt. With the engine running see if there is a "chattering" type noise coming from there - it can sound quite bad - replacing the tensioner is the answer.
This will have nothing to do with your oil problem - if there is water in the oil then it is either coming from the engine oil via the head gasket (same test get a compression test done) or it is leaking from the auto gearbox fluid - if it is that then it needs looking at quickly because you will also have water in the gearbox fluid which is not good news. If there is no water and you are just getting oil forced up then it is either blocked crankcase breather (not sure where it would block though) or it is worn bores / pistons.

 

[Dieselman]

(not sure where it would block though) .

PCV valve.

 

[ms500]

Has the noisy idle just started or has it got gradually worse? There is a tensioner for the V belt - on the front of the engine to the left of the front of the head and on the top run of the belt. With the engine running see if there is a "chattering" type noise coming from there - it can sound quite bad - replacing the tensioner is the answer.

I've only had the car a few weeks, it's been there pretty much since I bought it and doesn't seem to have changed.

I think the timing chain in general needs some attention. How much would replacement of the timing chain / tension adjustment cost at a good independent garage?

or it is leaking from the auto gearbox fluid - if it is that then it needs looking at quickly because you will also have water in the gearbox fluid which is not good news.

Funny you should say that; I've actually just got the car back from the MB dealer who fixed a leaking gearbox coolant pipe which went into the radiator.

 

[Smiley]

I have just re-read your first post ands there is one other thing you should check first - the OVP relay - a failed one of these (and they do fail) can cause all sorts of odd symptoms. The relay is located behind the black cover behind the battery and under the windscreen. It is mounted upright - not too big, if you pull off the black plastic cover you will see a fuse under a clear plastic cover. Check the fuse first - I am not sure how to check the relay other then substuting it. See if it is says made in Germany on it - I think this means it is an old one and is more likely to fail. No doubt someone else can confirm that.

 

[Smiley]

I've only had the car a few weeks, it's been there pretty much since I bought it and doesn't seem to have changed.

I think the timing chain in general needs some attention. How much would replacement of the timing chain / tension adjustment cost at a good independent garage?



I doubt it is the timing chain - unless the car has been seriuosly abused it should last forever (ish) - much more likely to be the tensioner on the front of the engine - it can sound like a worn chain.

 

[Ade B]

OVP would affect cold start, but I thought that the ABS light would stay on if it had failed.

Ade

 

[ms500]

The funny coloured oil. Was it mayonaise coloured.? If so that is oil and water mixed either as a result of the head gasket leaking or condensation forming in the breather pipes.

I guess it could be described as mayo, it was kind of light brown. I would have taken a picture if I thought it was significant but it's all been put back together now. The following picture is proably the best example of the colour:

http://www.artesanos.com/graphics/agfagress/overlook-light-brown.jpg

Check the coolant header tank, does it have any oil or mayonaise in.?

Looks a little grubby, but no obvious signs of oil or mayo.

 

[Smiley]

Funny you should say that; I've actually just got the car back from the MB dealer who fixed a leaking gearbox coolant pipe which went into the radiator.[/quote]

This is a very common pipe to replace because they corrode - I doubt that this in itself is anything to do with your problems. Good idea to put some grease or waxoil on the new pipe - stop it going the same way as the old one.

Is the oil like mayonnaise - or does it look like there is oil in the water in the header tank?

 

[ms500]

Is the oil like mayonnaise - or does it look like there is oil in the water in the header tank?

See my previous post

 

[Smiley]

Checking the PCV valve would seem like a good low cost easy start - could cause these symptoms. Perhaps dieselman can point you in the right direction.
Also check the fuse on top of the OVP (although I agree with the other post - usually the ABS light comes on as well); after that I would check the throttle flap assembly and give that a good clean round the edges with a cloth and some carb cleaner.
After that a good hard run - I assume the car has not done lots of very short journeys?
After that I would not spend any more time or money until I had done a compression test - at least you can then confirm that the engine is basically sound and it is worth spending money on.

ps do you have to top the coolant up at all?

 

[Dieselman]

http://www.detali.ru/cat/oem_mb2.as...GM=717.450&CT=M&cat=520&SID=14&SGR=030&SGN=02
158 is the partial load breather but here must be another one for idle.

Check all vacuum connections to the manifold as well for the poor running.

 

[ms500]

Checking the PCV valve would seem like a good low cost easy start - could cause these symptoms. Perhaps dieselman can point you in the right direction.

Where could I get a new PCV valve from? I presume I would have to remove the camshaft cover to fit it.

After that I would not spend any more time or money until I had done a compression test - at least you can then confirm that the engine is basically sound and it is worth spending money on.

I will get this done, since the engine also seems a little oily towards the front below the exhaust manifolds.

 

[Smiley]

I dont think you need a new one - more a case of cleaning the assembly and making sure it is not blocked - ie the crankcase can "breathe" freely and is not under pressure maybe dieselman can just clarify and confirm that for us. I think he also suggested running the engine with it disconnected to clear it out? Need to be prepared for it to make a bit of a mess if there is pressure in there though.

If you have an oil leak then it is either the classic MB head gasket failure - or it could be another symptom of excess pressure in the engine - which again comes back to either the blocked breather or worn engine.

 

[scooter]

can you adjust the chain tensioner with out taking the engine front of and what do i need to watch out for i know the alternator has to come of to do it
i drive a e230 w124 estate 91

 

[kth286]

ms500

Your 104 engine should not be filled with oil above the middle of the min and max marks on the dipstick when on level ground.

Merc issued a TSB on the subject, and it will reduce oil dribbles.