W124 Rough Idle

[Bean]

I have what seems to be a common problem with this car - rough idle. The car is a 1995 W124 E280 estate. M104 engine.
The car idles between 600 and 1200 and after 5 minutes it stalls. I’m not very mechanically minded but I would like to try and have a go fixing the problem without replacing every part! I have done some research on the subject (lots of posts) and based on that research this is what I’ve done:
Cleaned the throttle body – made no difference
Checked the fuse (30amp blade) on the OVP relay. The fuse was fine but I’m not sure how to check if the relay is okay?
Cleaned the MAF – made no difference
I’ve cleaned the purge / regeneration valve. Again no difference but I’m not sure if its working – no ticking noise.
I noticed in the service history that in 2012 the car had idle problems and the MAF was replaced with a used one which seemed to fix it – until now. (The loom was also replaced about 10 years ago).
There is the smell of petrol so there might be a problematic charcoal filter. Whilst I know what it looks like, I’m not sure where its located and once located how to tell if its working?
I have tried to build a reader but I haven’t had much luck! I’ve connected 1 lead to pin1, the other to pin 16 and the test lead to 8 and 14 but nothing happens but when I put the test lead into 10 or 12 the LED comes on permanently. http://www.peachparts.com/shopforum/tech-help/107630-e320-16-pin-dtc-charts-inc-pin-8-pin-14-a.html
Out of desperation I took the car to the local garage and they just told me it was 'complicated'! The closest specialist is a 2 hour drive away. Any help or advice would be much appreciated.

 

[hotrodder]

The charcoal filter is hiding behind the front nearside wheel arch liner and collects fuel tank evaporative emissions which are then fed to the engine via the purge/regeneragtion valve. The valve is only activated under certain conditions, above a certain coolant temp etc. Full details here... 47 Fuel system - M104 spread over several pdfs.

Have you tried running the engine with MAF disconnected? If so did it run worse or the same? Same deal with the purge valve but you obviously need to block the hose that goes to the engine or you'll have an air leak into the inlet manifold

Does the car have cruise control? This makes a difference to the throttle body/actuator (ETA) and to it's loom (whether it plugs into the engine loom or is seperate) which is the same comedy biodegradable type as is the wiring inside the ETA

While there may not be an MB specialist locally there must be a garage that can do better than 'it's complicated' because compared to modern stuff they aren't although i can see how someone used to plugging into OBD and doing what they're told could become stumped

Can you post a decent pic (showing all the details) of the blink code reader you built, there's not much to them but given the results it gave...

Is the petrol smell coming from the engine bay, near the purge valve or somewhere else? Finding the source of the smell would be my first priority

 

[WDB124066]

It is the black rectangular canister below the bonnet spring.

 

[Bean]

Thanks hotrodder for your response. I've tried running the engine with the MAF disconnected and it made no difference. I will block the hose on the purge valve and see if that makes a difference. The petrol smell seems to be coming from the back of the car. I'll redo the reader and see. Thanks again.

 

[Bean]

Thanks WDB124066 for the picture. Can the canister be cleaned or just replaced?

 

[WDB124066]

I'd say just replaced, they are a bit pricy though.

Back of the car sounds like fuel pump or the little hoses in that area, they do tend to let go there but once replaced seem to be fine.

 

[hotrodder]

The charcoal cannisters are just over £50 from inchcape, A1244700359. As WDB i don't think there's much you can do to 'em if blocked up. I can't see it directly causing the hunting, if blocked then the fuel tank venting would be affected which can result in the tank pulling a vacuum as fuel is used. The purge valve itself can cause hunting if it's say stuck open (like a vacuum leak) and ain't cheap new (just over £100) for what they are

If unplugging the MAF didn't make a difference then i'd say it's a suspect. If and when you confirm the MAF don't get a cheapnese one from the bay and if buying new don't bother asking MB, much cheaper if you shop for the Bosch part #

While one of the flexible fuel hoses between the tank and pumps is a likely suspect for the petrol smell check out the fuel filler neck where it meets the tank itself while you're under it and if it's solid splash some underseal/waxoyl etc about. On estates it's right in the firing line of crud and stones thrown up by the O/S back wheel and prone to rusting through. I had to repair mine a couple of years ago

 

[Bean]

Thanks hotrodder. I've found a garage who will read the codes and check for leaks via smoke. I found a used Bosch MAF on ebay for £30. But probably makes sense to buy a new one? I'll check the filler neck. Thanks Again

 

[hotrodder]

I wouldn't buy anything yet but if/when the MAF diagnosis is confirmed i'd happily take a punt on a (guarenteed working) used genuine one for £30 personally. New from MB they're over £250 (list price £290!!) from a quick look around the internetz Bosch 0280217500 can be had from Germany for ~£130 delivered. That's complete with the housing, if the hot wire sensor is available by itself should be cheaper?

 

[hfmscan]

I have tried to build a reader but I haven’t had much luck! I’ve connected 1 lead to pin1, the other to pin 16 and the test lead to 8 and 14 but nothing happens but when I put the test lead into 10 or 12 the LED comes on permanently. http://www.peachparts.com/shopforum/tech-help/107630-e320-16-pin-dtc-charts-inc-pin-8-pin-14-a.html

check voltage on DLC between 1 and 16. and between 1 and 8.
check fuse 7.
try diagnose with laptop and VAG COM USB KKL 409.1 (my signature)

 

[Bean]

Thanks hfmscan. Where is fuse 7?

 

[hfmscan]

on fuse box.

on england version:
http://www.team-bhp.com/forum/long-...0-w124-benz-bangalore-long-term-review-4.html

in the photo a lot of fuses and they all have their own number!

 

[Bean]

I changed the MAF with a used one and the high idling has gone and the codes on pin 8 are all clear. the car is a lot better, no high idling BUT there is still some low idling which is a worry. The code tester for pin 8 is all clear (problems with air bags and central locking but I'll leave that for another day....). Any thoughts?

 

[hfmscan]

buy or get USB KKL VAG 409.1 and made diagnose and send me result...
This is easier than guessing on the coffee grounds.