Stalling 300E, Idle control?
 

Does anyone know how to test an idle control valve on a 300E?
Other than listen to a long screwdriver at the ear?
I am working on a '91 300 E w/156000 miles and the 3.0 liter engine.
It has just had the injectors, cap & rotor and plugs changed. Fuel pressure is @ 82 Psi. and it has plenty of spark. These were all changed because of a stalling problem the car had where it whould just die with no warning, but usually start right up again. Currently it will start and idle but it has a hesitation @ 1200-1400 rpm. when the acclelerator is first applied. Once past that it revs fine until let off. It also dies when a load is applied, (as in D) however, not in reverse. It studders and coughs in R when the accelerator is pressed.

There are not fault codes coming up on the tester. It appears to be a fuel related issue, but not sure... any suggestions or help would be appreciated.

Thanks

Does this happen with the engine warm or cold? Continuously... always stalls?

I suggest you do a forum search on the following word: "Potentiometer".
The stalling issue has also been tracked to that component.

How old is your OVP - overvoltage protection relay?

Remove it, then skake it, being sure to hold the clear plastic flap down. If you hear rattling, replace it.

http://www.peachparts.com/shopforum/tech-help/37410-ovp-question.html?highlight=ovp

It does not seem to make any difference whether it's cold or not, it always sputters at first when the peddle is pressed. And it always stalls when placed in D, so far.
I will try the OVP, I didn' t think that's what it would be because all of the lights and electronics work. But I'll check it and let you know.
I find it interesting that the "Potentiometer" was pointed out because the first time car started having trouble is it was also turning a corner. hmmm, coincidence? I am not entirely sure what that would do, but anyways...

You might want to unplug the EHA to see if the computers fuel signal is 'out of whack...

Why yes, it might be.
 

What a coincidence that you should mention the EHA. I neglected to state that when the car first started having these problems, the EHA had started to leak and I had to replace it.(new one) I forgot to mention that....
So I will go unplug the valve and see if it makes any difference. But what will I be looking for? How do I test to see if the signal is wrong or not? Does that show up as a fault code?

Thanks,
Nathan

The easiest way to diagnose this problem. Key on engine off, pull the plug from the idle control valve, if you feel it switching, means you have power. If you do not feel it switching when you connect/disconnect the terminals, you have 1 no power to it, or 2 seized. To check power get a test light and check the yellow and brown, I think thats the wire for power. If you have power great, you have a bad valve. They are not cheap. If no power, go after the Overvoltage relay. It has a fuse at the top, and Benz has issued new relays that superseded the old ones. Thats probably going to help you out, if not, post back.
GVB

If not haveing the EHA connected cures the stalling problem then you can be somewhat convinced that there is a problem with the computer or one of it's input sensors (O2, coolant temp,... ) or the EHA itself. The EHA is the only mechanism by which the computer can make adjustments to the fuel mix.

If you have a volt meter you can read the duty cycle between pins 2 & 3 at the X11 diagnostic connector. This signal is representitive of the leaning or richening being made by the computer, through the EHA. This measurement is made somewhat eaiser if your multi-meter has a duty cycle function, but it can be extrapolated by measureing only volts.

But before we go down that path try disconecting the EHA to see if that affects your condition.

Adjust the throttle linkage, and make sure the coolant temp is good. If it is near the envelope, replace it. There is a microswitch at the stop of the throttle linkage, make sure it is ok, thats the decelerator so to speak for the EHA.

Ovp
 

Well I disconected the EHA valve and it seemed to run a little worse....
Checked the fault codes again after I reconnected the EHA, and nothing showed up.
After that I pulled the OVP relay and it just happens to rattle.... Hmmm.
So I will replace that and then let you know what happens. If that doesn't work I will try the microswitch, as that is the type of symptom it is having. (coughs just at the point where the switch would be actuated) I really can't be certain what the problem is, but I will try all suggestions until I find it!
Oh, and one more thing, I can only get it to rev when I just barely press the throttle.(slow roll-on, about 1/4 of the way) If I mash it, even at 3500, it coughs and sputters.

Thank you, guys!
Nathan

That sound like you have a bad air flow meeter. Do you have a volt/ohm meeter?
GVB

Bad air flow meter is consistent with the earlier comment on potentiometer. This is one of the few cars with a separately available air flow meter potentiometer - usually about $50. If Phil (above) does not have it you can try Mercedesparts.com.

Ok, so how would I test the Poten. with a voltmeter? And more importantly, WHERE is it located exactly? I read somewhere that it is under the fuel dist. but is the MAS part of the same unit? I was informed this might be availible seperately. I read about cleaning the contact strip with an erasure but I'm not sure what I am looking for. What should the readings be with a voltmeter?

I just replaced the OVP relay and tested the volts to the idle control valve which was reading about 5.9 volts when running and 2 volts when key on, engine off. I tried disconnecting the ICV but I could not hear or feel a noticeable click or sound. It seems like it made a sound when I listen with a screwdriver, but thats it. Could this be a problem?

Thanks,
Nathan

Do a search above for potentiometer - there's several good threads. Just follow the air intake until you get to a butterfly valve. Buy the part first and you'll know what you're looking for.

Here is my story...
 

hopefully this will be helpful

--------------------------------------------------------------------------------

I had a 88 300E .when the hotter weather came the car started to stall for no reason.changed the voltage regulator , a few other things.Make the long story short..someone at mercedes told me to take out the computer(behind the battery , under the hood) The car will start up in a kind of safe mode(higher fuel consumption, slower acceleration but IT WILL GET YOU HOME!!!...lol BTW show me another car which will do that!!!) Now if you drive the car around for a day or 2 and the stalling doesnt reoccure, the problem is 99% with the computer.You can get a new one or used one but what i did is......... (i remembered that german printed circuits gave my problems already before ,poped up printed circuits,loose soldering joint,)...took the comp out,seperated the 2 inside panels and reheated all joints ...appr 200.....and drove the car for another 150000 no problem.But thats just how i solved it.

good news
 

Well guys, this is interesting. After all that I still don't know what it was for sure, but now it is running like a champion. The last part I tried was the OVP and that did not seem to make much or any difference. I was about to take apart the intake assymbly and look for the Potentiometer, so I took the idle control valve off and tested it just to be sure and it seemed to work as it should so I put it back in and what do you know, it seemed to do something because now the car is working the way it should. hmmm
Well thank you to everyone who has helped me with this perplexing problem and I now know more about my car than I ever would have....
I also have the information for any future problems that might arise.

Thank You!!!!
It is all very much appreciated....
Sincerely,
Nathan

Maybe you jarred some crud loose in the ICV. I would take it off and clean it out with carb cleaner, just to be sure. They get pretty dirty from the crankcase gasses going through.

ha ha
 

Should always check co2 adjustment first after replacing a E.H.A. valve. Make sure your o2 sensor is good when doing this.

300E surges then quits
 

Help!!! I have a german 1985 300 E. They say its the same as 1986 US. Its a 6 cylinder fuel injected. It runs about 20 minutes then starts surging real bad upon acceleration, then it dies, completely everytime you just barely touch the accelerator. It will start right back up but will not move much if you have to press the accelerator. I live in Costa Rica and parts are VERY EXPENSIVE. I have replaced fuel filter, cleaned injectors, replaced fuel pump, and today the (Dosificadora) which is I think the fuel pressure regulator. Its the part that the fuel lines come out of to the injectors. New this part costs here $2000. Rebuilt $1000. I found a used one for $350. but when installed ...nothing ...no change. the mercedes mechanic feels real bad. But ???? I have read here about oxygin sensors, catalytic clogs and crankshaft sensors as being maybe the problem. I can't keep buying parts so really need help on what to do now. Its Friday night and I have an appoinment with my Baby and the mechanix Tuesday. I love this car.
Bill