C36 AMG hunting at idle - MAF?

[callahan]

Hi

I'm getting my brother's AMG checked out this friday before I make him an offer and I've noticed an odd issue when at tickover. The revs move up and down a bit, but you can feel the car rocking slightly as if it's trying to pull away - bit like I imagine a V8 engined nascar would on the starting grid!!

My only guess is that there's a fault with the MAF and I'm sure this will be checked on friday, but is there anything I can do to check it first? Can I just unplug the sensor or do I need to remove it entirely to see if it still happens?

Either that, or are there any other ideas? Apart from that it drives beautifully and I can't wait for my trip to the south of France in June with an overnight stay in Le Mans, of course

Thanks

 

[Alps]

hi, yep, sounds like the MAF to me, but it could be another sensor giving the MAF a bad reading.

where in north essex are you?

 

[callahan]

hi, yep, sounds like the MAF to me, but it could be another sensor giving the MAF a bad reading.

where in north essex are you?

I live in Saffron Walden, which is north essex, but about 10 miles south of Cambridge.

I'm taking it to Autokare in Cambridge on friday, but wanted to be prepared for what he was likely to say.... and how much it might hurt (my wallet)

 

[Bobby Dazzler]

Oxygen sensor gets my vote.

 

[callahan]

Oxygen sensor gets my vote.

Any idea of rough cost?

Thanks

 

[Bobby Dazzler]

No idea I'm afraid, although someone is sure to have had one replaced recently.

Certainly not megabucks though - and probably cheaper than MAS/MAF!!

 

[television]

If you unplug the MAF then you take it out of the equitation

 

[callahan]

If you unplug the MAF then you take it out of the equitation

Is that just a case of unplugging the connector that goes into it?

I'm not the most techie of people (believe it or not ) but I had a look and there is an electrical connector that goes to the maf, presumably unplugging it stops the maf from working?

Worth a try to start with I suppose....

Thanks

 

[television]

Is that just a case of unplugging the connector that goes into it?

I'm not the most techie of people (believe it or not ) but I had a look and there is an electrical connector that goes to the maf, presumably unplugging it stops the maf from working?

Worth a try to start with I suppose....

Thanks

Thats the one, if it stop surging, then you will know

 

[callahan]

Excellent, I'll give that a go tonight.

Thanks

 

[BlackC55]

It could be a air leak too.....

 

[callahan]

It could be a air leak too.....

Any simple ways to check for this? Or any obvious locations to look at?

Thanks

 

[television]

On the intake side of the engine there are some plastic pipes going here there and everywhere, its those, jently moving them you could find something

The engine pipes are in the link
http://www.detali.ru/cat/oem_mb2.as...GM=717.441&CT=F&cat=44V&SID=80&SGR=015&SGN=01

 

[callahan]

Thanks. My appointment for tonight has just been postponed, so I'll be able to have a look in daylight, which is nice.

I will report back my findings.

Cheers

 

[callahan]

Right, been having a bit of a play as suggested.

To start with the engine revs hover around the 750 mark but the car shakes from side to side and the rev needle probably goes up by 10 then down by 10 and so on.

I unplugged the maf sensor and the revs went from 500 to about 1000, down to 500, up to 1000 etc but without the 'shakes' - I assume this means the maf is working correctly?

Had a bit of a look at the engine pipework and could only see one thing that looked odd - is this supposed to be open??

Looks very odd to me.

Unfortunately it started raining and I haven't washed the car, but here's a quick pic:

 

[callahan]

Here's a better pic of the strange bit:

Cheers

 

[Alps]

there is another pipe which is supposed to be connected to that to end up between the headlamp, its the intake pipe. This wouldnt effect the idle though. if its going up and down by 10, then it sounds like maf or oxygen sensor to me

 

[callahan]

Thought it was a bit odd, don't suppose anything could have clogged up the air filter then? That might cause it....

Thanks

 

[television]

Do you have parts 158,161 etc

http://www.detali.ru/cat/oem_mb2.as...GM=717.441&CT=M&cat=520&SID=09&SGR=015&SGN=01

 

[callahan]

Nope, that's where it ends!!

Wonder where it all went to.....

Any pics of what it should look like?

Maybe I should take a pic of the whole engine bay just to make sure nothing else is missing!! engine etc.....