W124 Warm Idle Issue

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reysongz

New Member
Joined
Jun 16, 2014
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7
Car
e320 W124
Hi, I bought my W124 E320 last week, and I must say I absolutely love it. However, when I picked the car up it has a slight issue with the revs dropping when putting it into D or R from P. This would sometimes cause the car to stall.
That being said, the car runs beautifully without fault and exactly how it should.
I thought I would treat the old girl to some new spark plugs which might fix the issue and also clean out the butterfly for the throttle body, the breather that goes across the rocker cover and the MAF sensor, but it seems I was wrong.
I now have the problem of once the car is started and been running for around 90 seconds, the cold start solenoid/relay switches off and the car cuts out.
Ideally, I just need to increase the idle rpm by 300-400 but I have no idea on how to do this. It's not as simp as it was on the old 300ce where air/fuel mixture was controlled by a simple screw.
Can anybody assist with this? I'm based in the Bedford area.
 
There are some basics to check. Is there an air leak? These have various breather hoses that perish over time.

Next in line is idle control valve.. Lots of used ones on eBay, recommend three pointed parts for stuff like this as he actually tests his stuff before sending.

Then check idle co level, you need a mot garage to help with that one. If too low it can be adjusted with an Allen key down the middle of the air filter iirc.

There is no idle speed adjustment as such on this model.

Good luck...
 
Thanks for the reply. Being the later style coilpack engine, there's nothing to adjust through the air filter. I'll try an idle control valve off ebay...

Edit- just had a look on eBay for "e320 idle control valve" but no joy. Can anyone assist?
 
iirc you will have drive by wire throttle on the later m104, which also controls the idle.
 
Has the wiring loom been replaced on the car?
 
What year is the car?
What's the mileage?

I had this on a '96 320TE I got a couple of weeks ago, I replaced the voltage regulator (the gadget on the alternator with the brushes) and fixed this issue and a couple of others too.
I had intermittent warning lights, generally rough running, the stalling issue you mention and the temp gauge was all over the place.
 
just had a look on eBay for "e320 idle control valve" but no joy. Can anyone assist?

There is no idle control valve as such, the throttle body/actuator is used for idle control i.e. it's (at least*) partly electronic and controlled by the ecu as said. No mixture or idle adjustment screws at all, it's all done by witchcraft

There's a looooong list of things that can mess with the idle on these, first on the list is the wiring loom already mentioned. If it's still on it's origional comedy biodegradable loom then until that's been checked/repaired/replaced everything else is pretty much a waste of time as the insulation falls apart. Wiring in the throttle actuator is also prone to falling apart. As you've changed the plugs this needs checking sooner rather than later really as disturbing the wiring to the coil packs can result in damage to the ecu if the insulation on them is fubared and they short out.

Checking (and clearing followed by rechecking) any fault codes is worth doing as it may narrow things down, for example a fault with a temp sensor (or the wiring to it!) fits what we know. List of codes and a diagram for a home made blink tester in this thread... http://www.mbclub.co.uk/forums/engine/122237-m104-280-engine-misfire.html which also discusses the fuel tank venting system that can mess with the idle

What is the idle speed, both when you bought it and now that it's worse? does it hunt before stalling or just die without trying to 'catch' itself?

* Having cruise control etc = more leccy control over the throttle
 
is your car the earlier 320 with the air injection pump

OR

the later 95 year (approx.) with it deleted ?????????
 
To be honest guys, I don't know too much about this engine as my previous mechanical knowledge has been gained through working on volkswagens and subarus. I've checked the wiring loom and it seems to have been changed as all of the wires I have found look fresh. I don't know if the car has an injection air pump as I have no idea what it would look like.
The rpm on idle varies. When I picked the car up, it would hunt around 600-900 and sometimes fall below this is stall. Now I've changed the plugs and cleaned the throttle body system it idles at 1300 when cold and when warmed up drops below 600 and cuts out.
I've checked the engine bay for signs of a vacuum leak but in all honesty I'm not sure where to look.
I've ordered an intake temp sensor as my current one had seen better days. I've also ordered the box which sits between the intake manifold with the throttle solenoid (sorry I don't know what it's called).
I'll try these and see how I get on. it would seem I just need the car to idle higher, as it runs perfectly apart from the idle problem
 
Sounds like good news on the engine wiring loom front*. If it has an air injection pump it'll be sited above the alternator at the far left (looking into the engine bay from the front) of the poly vee belt run. Just below and left of the top idler pulley. There'll be a diagrams in the owners handbook or google 'w124 m104 serpentine belt route'. The air injection is only used for a minute or two after starting a cold engine and is (usually at least) noticable due to the clatter it makes

The box that sits between the intake manifold and throttle body... sounds like you're talking about the resonance valve? (circled in the drawing below)

There's a bunch of vacuum lines to find and check, googling m104 engine engine vacuum leak will get you diagrams like this...

249665d1356177916-hesitation-3500-rpm-m104hfm.gif


Y58/1 purge control valve is the fuel tank vent mentioned in the other thread which should only be activated under certain conditions and can cause a rough idle with hunting if it isn't working properly. Function is described here... http://www.w124performance.com/service/w124CD1/Program/Engine/LHIS/47-0200.pdf and an easy/free thing to test- simply disconnect and block off it's feed to the engine as described in the thread i linked to yesterday

Personally i'd be getting the fault codes checked as it might save you a bunch of time and money compared to randomly replacing parts

* replacement engine loom doesn't necessarily mean that the throttle body isn't full of rotten wiring that'll stop it from working properly though
 
I've got access to a snap-on OBD2 scanner but I thought the W124 doesn't have an OBD2 port...? Has anyone local to the Bedford area got a blink tester they could lend me?
 

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