W211 Cdi

[GEH007]

At a steady throttle and travelling at say 40 mph, the rev counter flickers around a little and you can feel the engine and car "surging" ever so slightly in line with the rev counter flicking up and down.

It's really not by much but clearly isn't quite right.

Any ideas out there of what the cause may be?

Thanks.

 

[BlackC55]

Thats a tricky one. What engine is it?

 

[GEH007]

Oh sorry, its the 220 cdi.

As I say, it's only a fairly minor flickering but you can feel it and see it on the rev counter.

Cant be much I wouldnt have thought but would be nice to solve it!!

Thanks

 

[BlackC55]

Slight missfire maybe. If it is I would be looking at the injectors as maybe the problem. How many miles?

 

[GEH007]

It's done just short of 70k.

Is there any recommended way of cleaning/flushing the injectors on these?

Such as an additive followed by a good old fashioned "Italian Run-in".....

 

[BlackC55]

You could try some diesel injector cleaner. You really need it looked at by someone who knows them well.

I am only guessing at the injectors it maybe somthing else. It is very difficult to say without seeing/feeling it.

 

[GEH007]

Thanks for trying to help.

I'll try to elaborate.

Lets say usually the engine holds 2000 rpm at a steady 40 mph.

What actually happens at a steady 40mph is a rapid fluctuation in the revs between say 1900 and 2100rpm. You can see the rev counter flicking up and down to reflect this and feel the engine rising and falling the same.

 

[BlackC55]

Is it an automatic?

 

[GEH007]

Yes it is.

 

[BlackC55]

It maybe gearbox related also. The atf level is important so get that checked.

Have you considered the air mass sensor maybe at fault too? Has it ever had one?

 

[GEH007]

I've no idea. Only had it a couple of months.

Its a great car with full history in great condition and drives like a dream; just this little issue.

Would it need one by now at that mileage?

Thanks again for your help.

 

[BlackC55]

They are almose a serviceable item. They go wrong ALL the time. Cheap enough from Euro Car Parts. Make sure you get a direct replacement.

 

[GEH007]

Ok, will give that a try first. What exactly are they called?

And the ATF level, is that something I can check or is it a specialist job?

Thanks

 

[BlackC55]

You need a special dipstick. Specialist or dealer only.

They are called an Air mass sensor or some people call them a MAF.

 

[GEH007]

Thanks again, good of you to help.

 

[BlackC55]

Where do you live?

 

[GEH007]

An update:

Thought id try something today and was interesting.

Same 40mph speed, but used the speedtronic crusie control and guess what? It doesn't happen.

So, I presume that rules out dirty injectors?

What about MAF or auto box? seems odd I know.

 

[GEH007]

An update:

Thought id try something today and was interesting.

Same 40mph speed, but used the speedtronic crusie control and guess what? It doesn't happen.

So, I presume that rules out dirty injectors?

What about MAF or auto box? seems odd I know.

Any thoughts on my update would be greatly appreciated.

Many thanks

 

[BlackC55]

Have you had the AFT level checked?

 

[BlackC55]

***atf*****