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.