Hello everyone. I have spent hours searching for the answer to my question and have yet to find a decisive one. This will be a very detailed post, but since W124 idle problems are so common, complex, and elusive, I think you guys will need lots of info to help.

My car is idling very roughly. About 3/4 of the time, when I start the car and watch the tach, the rpms jump like they used to, but instead of stabilizing at around 800, the car immediately dies. If I give it gas and rev it up once or twice, it sits at around 500 rpms and the car shakes like crazy. When I accelerate, I will get some hesitation only when I accelerate somewhat hard (but not all the way to kick down).

From my research, the idle control valve sounds like the most viable culprit. THe mechanic that had the car for the last few days said that is the next thing he'd check. I took the car in because I BOMBED emissions (not even close), and I assumed it was related to the rough idle. Unforunately, it wasn't.

I am in a whiny mood, so I'm going to give you all my recent service history (last 2 yrs). I have given my beloved car so many chances and probably should've sent her to the junkyard long ago. Oh well.

-Fuel distributor replaced
-rear main seal replaced
-head gasket replaced
-valve job
-oxygen sensor replaced
-drive belt tensioner
-new motor mounts
-replaced all injectors
-BG44k fuel system cleaning
-Distributor Cap
-Rotor
-ignition coil
-crankshaft position sensor replaced
-hydro accumulator valve replaced (attaches to fuel distributor)

Other hints, since the mechanic made detailed notes:
-Check engine light is on, code is G312- "Oxygen sensor shorted to positive, MAS Fuel pump relay circuit 87 not functioning"

-they said "tested fuel delivery rate excellent at 1000ML at 60 PSI in 30 seconds.

-they said "idel control valuve appears faulty; causes sticking high idele. When unit is unplugged and then plugged in again to wiring harness, idle regains proper RPM".

My research says that the two most common culprits are the idle control valve and the Over Voltage Protection (OVP) replay.

For a complete newb who is sick of spending so much money (over $8k in repairs), is the idle control valve easy to replace?

Can anybody give other insights or potential problems?? I'm an inch away from sending this heep of ***** car to the junk yard.

I'm not sure from your thread if all the parts you replaced were in an attempt to resolve your current problem or because they needed replacing due to other symptoms. Let me recommend that you take your 300CE to a MB-trained tech or to a local MB dealer's Service Department ... either one should be able to diagnose the cause of your rough idle and make the appropriate repair. Throwing parts at a problem is never a good idea and becomes very expensive. You don't mention replacing any vacuum lines/hoses ... I'd suspect leaks in old, dry-rotted hoses could be attributing to a rough idle.

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Fred Hoelzle

As you mentioned in your post - these rough idle issues are indeed very elusive. Still from reading your post I would consider doing the following before getting rid of the car or setting it on fire..
Clean the idle control valve and replace both hoses leading to & from it if they are dry and brittle (most likely).
Replace the plug wire set if this has not been done in recent years. If you search under my name you will find details on doing just that.good luck

I would clean your ICV with brake cleaner and lube with WD-40, then check the hoses for air leaks and replace if necessary. Pop the hood at night when it is pitch black and see if the wires are arcing. Check out my experience: http://www.peachparts.com/shopforum/showthread.php?t=162549&highlight=wires+arcing

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Thanks very much for your replies. Ferdman, sorry I didn't make that very clear. Most of that stuff in the above list was done at the time I had the head gasket fixed... They weren't necessarily done to fix the rough idle.

I also forgot to mention that the plugs and wires were all changed when the distributor cap, rotor, and coil pack were done...

The ICV sounds like it's probably the cause. I don't want to take it to the mechanic if it's something I can do myself... it sounds like it is. Although I did read that the hoses attaching to it can be pretty tricky to replace... So I might have to take it in after all...

I looked really hard for a DIY on the ICV cleaning and I couldn't find one. There's lots of general discussion about it, but is it just as simple as unplugging it, scrubbing it off with carb or brake cleaner, and putting it back in? from the pics I've seen, it looks like there are two hoses and some wires that connect to it.

Also, is it under the air cleaner on the 3.0L 24-valve like most other 124's?

Thanks again

Peter

You'll want to soak the ICV overnight in something like WD40 or liquid wrench to really get the thick gooey junk out of it. The fluid will also lubricate. For best results, cap one end with tinfoil and rubber bands, then fill the whole ICV up with fluid. Dump it out the next day and you may be surprised at how black the fluid is. Be sure to blow it out with air.

The little shutter inside often gets stuck with crud and will not allow the proper amount of air to be metered. When the hoses to/from are brittle, they also allow unmetered air into the system which roughs up the idle quite a bit.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

great, thanks for the reply. so is it as simple as just taking off the air filter assembly, unplugging the thing, soaking it overnight, cleaning it off, and plugging it back in?

I think I will try this tomorrow. I don't want to spend 300 bucks on a new ICV and 100 bucks on an hour of labor... just not worth it if I can do it myself!!!

okay, I got at the ICV and cleaned it out. The car no longer dies at all, and the rough idle is no longer constant. It's back to more of a hicup that comes about ever 2 seconds. The hesitation is much better, but still exists.

The ICV didn't look too messy, although once I cleaned it I noticed that the valve opened and closed much more easily. Could there be something else about the ICV that could be causing my problem, or should I move on to something else?

The vacuum hoses leading in and out of it seemed pretty new- they were very flexible. However, they weren't attached to the ICV with any kind of clamps, and I found it pretty easy to pull them off and put them on. Could this be a potential issue?

Would it be a good idea to test the voltage of the ICV somehow? If so, is it a bad idea to do it with the air filter assembly removed? And what voltage would be considered reasonable?

Thanks!

It depresses me to see someone spend so much money on an old car. The fact that it is still not running right is even worse. My sincere advice is to sell the money pit and purchase another car that will fair better.

Good luck

i hear you man. I'm a CPA, so on the one hand I completely understand how stupid I have been financially. On the other hand, when this car runs well (which it has for brief periods), it's a true joy.

A CPA should also understand the concept of sunk costs and how they should not influence your future financial decisions... But the psychology fo it is really tough. I totalled up all of my invoices the other day, and I've spent $9,500 on "necessary" repairs over the last 2.5 years. And each time I took the car in, I thought to myself things like "it's a mercedes- it will last forever" and "I just need to do this repair and I'll finally get the car running well for another 100k miles." The sad truth is that it doesn't seem to ever get better.

The car has depreciated about $1,500 since I bought it for $5,500. Not to mention, I've put lowering springs on, euro headlights and taillights, blacked out the grille, and installed a very nice custom stereo system.

If I sold this car right now, I would take probably a $15k loss. Ha ha, so it's not that easy. I sound pathetic, but I can't help but think that the car will eventually run right. It's a machine! There should be a solution!!!

Since You Already Spent So Much Money I Would Get New Ovp Relay As They Control Many Engine Functions And Just Plug In. They Are About $65 And Have Updated Circuitry. Make Sure Your Motor Mts Are Ok. I Speak From Experience. Often Plugs Go Bad Quickly And Make Sure You Replace With Bosch Coppers. Nothing Else. Good Luck. Ours Drives Like The Beast It Was Meant To Be. Eats Up Spark Plugs, Though.

motor mounts have been replaced... but the OVP relay was definitely the next thing I was going to consider. Thanks for the input!

Hey guys. Thanks for your past input.

I got back from my honeymoon on Saturday and I bought an OVP relay (or "overload relay") from this site. I have to say, shipping was incredibly fast. I ordered on Monday afternoon and got it on Wednesday afternoon. I recommend the fastlane, and I'll do business here again!

Anyway, yesterday before I installed the new OVP relay and after my car had sat for about 10 days, it refused to start. This is the first time my car has ever done this, but for weeks leading up to yesterday, I had to crank it probably 5 or 6 times in order to get it to fire. And when it did, I would have to rev the engine to get it to keep running.

I was freaking out. I installed the new OVP relay, which was very easy. The car started up just fine on the first crank, which made me happy.

Although my rough idle is drastically improved, it's still noticeably present. Furthermore, my hesitation problem is less consistent (it used to hesitate every time I accellerated starting at under ~2,500 RPM), but when it occurs, it is just as bad as ever.

When I first started the car, the check engine light turned off. Which also made me happy. But then it turned right back on after about 3 minutes of driving.

So, things have improved- the car starts right up on the first try without any effort, and the rough idle is about 50% better. Overall, I'd say the hesitation problem is the same as it always was.

When I took it to the mechanic, they said that I have excellent fuel delivery. So that would rule out the fuel pump relay. They also said I was getting strange readings from the Idle Control Valve. As a reminder, I cleaned my ICV it works very well mechanically, from what I can tell (the valve moves smoothly and freely). So I figured that since the electrical current to the ICV comes through the OVP, the strange readings the mechanic was getting very well could've been due to a bad OVP. So maybe it's a bad ICV still. I have also read about people having bad vacuum hoses going in/out of the ICV, but when I looked, my hoses seemed pretty new. They were very soft and flexible.

I talked to another mechanic and he said it could very well be a vacuum leak. I would probably have to take it to him to figure that out since I would have no idea how to track that down.

What are my next steps? My car was adjusted to pass emissions about a month ago, which drastically increased my rough idle and hesitation. Could this be a tuning or mixture issue? I.e. could it be adjustable?

Thanks so much for your help, everyone. This car is darn near driving me to bankruptcy!!

sounds to me as though you need to undo the "tuning" that was done to get the car thru emissions.it may be adjusted too lean [3mm beside the fuel distrib]this would explain your symptoms completely.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg

man, I sure hope you're right.

My mechanic told me yesterday that he feels bad for me, so he'll go through the car and give me a free diagnosis. Maybe if I'm lucky he'll tinker with the mixture or whatever for free. The mechanic that got me through emissions (not the same mechanic, since my regular mechanic isn't certified to do emissions repairs) had to replace the hydro-accumulator valve (I think that's what it was called) because it was broken and made the mixture difficult to adjust. So maybe that's all it needs. But the same mechanic also tested my fuel delivery and he claimed that the pressure was perfect.

I'm probably an idiot, but where is the fuel distributor? I'd like to tinker with this myself, if possible. Any additional advice here?