John, no resistance values for it. It's obviously a variable resistor or "pot", but if the voltage goes up steadily as you open the air valve, then it's probably not the culprit.

I reread your posts, you say the car began to run okay for awhile after new plugs? Then started to mess up again? That's probably not due to you installing resistor plugs - most things I read indicate the resistor plugs run fine for quite awhile (or forever) but may damage the ignition eventually. I ran some in mine waaay back, before I was told of the potential problem, I saw no issue.

So, "maybe" it's fouling the plugs quickly, you said smoke was coming out.
If it smells funky, could it be coolant?
How about this.... engine got pretty warm in the slow traffic, the old head gasket gave up (this is VERY common issue on 103 engines) and it's allowing some coolant into one or more cylinders. This is making the engine miss and causing all sorts of starting/running issues.
Why don't you pull the plugs again and look for any clues on them?
Look for white smoke.
Look for bubbles in the coolant reservoir.
Do a compression check.
Look for milky oil.
Look for coolant leaking externally through the head gasket back by #6 spark
plug.

If it's a head gasket, you should be able to find it. And you better fix it fast if coolant is getting in. The head is Al, the block is iron, so the head gasket scrubs itself to death from expansion about every 100k miles on these
engines. Not too hard to fix.

Let me know what you find; if you need to redo the head gasket, I can walk you through it.

Of course, this is all guesswork on my part, it may be a dis-combobulated Flamerstam or something.

DG

Yes, the voltage values seemed to rise when the throttle is opened as expected...Although I did notice that when I let go of the throttle, the value jumped pretty high, then settled back to where it should be...not sure if that's normal or not.

Also, I'm quite sure the head gasket is fine...since I have had LOTS of BHG experience with my 3rd Gen Toyota Supra turbo...which also has an inline 6 and blows head gaskets pretty much constantly LOL. This car shows absolutely no signs of a blown head gasket...and I've smelled coolant being burned before, this car is making a different smell entirely, I'm assuming it's unburned fuel. Plus, coolant won't foul plugs...in fact, it usually steam cleans the cylinder it's been leaking into...so I'm pretty sure that isn't the problem.

The CEL is still lit tho, which means there HAS to be a problem with the Air Mass Meter...unless the ECU is really the culprit, but I'm assuming that they don't go bad too often?

Does the manual say anything else at all about the Air meter? Thanks!

edit: I should also add that I was looking at the old plugs I pulled out of the motor earlier, and they look like they have a hard grey coating on them that I can chip off with my fingernail...only on one side of the electrode...the other side is much cleaner...they are all like this. I'm guessing this is carbon fouling?

I have also noticed that after just 300 miles of driving, the car is starting to become progressively more difficult to start. I'm guessing this means that the plugs are starting to foul?

Doesn't sound like it to me. Could it be oil fouling because of valve stem seals? Look at these links and tell us which picture is closest to your plugs:

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

http://www.centuryperformance.com/spark2.asp

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

Well, no other stuff in the manual about the air valve sensor. It's just a simple Potentiometer apparantly.
Not actually having checked one myself, I can offer little help about how it affects the engine controls.However, with the motor idling, if I push the air valve gently down and hold it down, say, one millimeter or so, it will stumble, then recover and smooth out.
What is happening is the air valve controls the fuel delivery thru the fuel distributor; when you push down you increase the fuel, then the EHA compensates and reduces the fuel. But don't know how the air valve sensor data plays into the computer reactions. I assume it's similar to a GM throttle position sensor, where the timing and fuel enrichment are controlled in relation to the throttle opening.
- OK, not a head gasket. And apparantly not the air valve sensor.
Let's think some more.
- These engines can dirty up plugs in a hurry, particularly if the valve sterm seals are leaky. But 300 miles is a bit extreme. I see that type of buildup beginning after approx 2000 miles, but I have really good stem seals and 1/2 quart oil usage in 5k miles.

Maybe, it's running really rich; smoking, fouling plugs, and the code 4 just happens to be what it set because it expects the air valve to be open more;
or code 4 was set because the German engineers think differently (Ha).
We (you & I) really don't have any info about why/when these codes set. So maybe it's not the fault of the air sensor?
Maybe the EHA valve is richening it up, and system is trying to react, but can't lean back down; so it stumbles, fouls the plugs, starts hard cause it is flooding slightly?

I guess if it was me, I would check that on/off ratio with the Sears meter, as I outlined above. That can check so many evils, such as the enrichment EHA valve, the O2 sensor, the fouling plugs, the entire fuel delivery system basically.
Also, check this out! There is a chart in the manual that outlines a series of probable faults, depending on what the ratio reads. If you check the ratio and report, we can possibly narrow it down.
Example: a constant 40% reading indicates a problem with, guess what, the air valve sensor. A constant 30% indicates faulty coolant sensor. etc, etc.

So, humor me, go buy that meter and plug it in!
I'll stay with you on this (at least until the antibiotics kick in and kill this cough, and I can play golf again!). Just kidding, I want to learn something about this, too.

DG

OMG thank you so much!!! I will go try this right now.

Ok, I just did the test...and the voltages are dead on within specs...is there any way to test the resistance of the sensor itself? Does the manual state what the resistance values should be?

Haha! Thanks for your continued patience! I will probably go buy one tomorrow, if not tonight...I need to have the car smog tested, and a CEL is an automatic fail...so it's kind of a priority right now. I also went to the junkyard looking for an air mass meter today, there were 5 W126's, 3 Diesel, 1 V8, and one 300SEL with a missing motor -_-. Typical.

Anyway, here is something to occupy you until I get the meter and test the ratio.

A couple pics of the car you're helping fix!

Ok, I went and I took some pics of the plugs...they look a bit different than I remember, it looks to me like they are a combination of oil and carbon fouled...

Read this thread:

Spark Plug Horror! Look!

Do those pictures look familiar? You probably need valve stem seals.

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

Wow, you got all that in 300 miles? Mine look just like that in about 10k miles, and I thought that was pretty bad. But, I've pulled them out looking that bad, and the motor was strill runnung great.
Before I got the valve job at 100k miles, mine burned a quart of oil in 250 miles on the highway, but not so much in town (the oil pumped into the head at high speed and flooded the valve stems I presumed).

So, yeah, you probably need the valve seals, but I have a feeling there is more to the problem, based on your recent experience. Those plugs look bad, and they appear to be platinum tip, which may accelerate the problem.
But, if you installed those new plugs, and car runs great for only a few hundred miles, then maybe it's a combo of bad seals, over-rich, and weak ignition.

So, I kinda back to the original hypothesis - throw in a cheap set of std plugs (non-resistor if you can find them), see how it runs immediately. Check the on-off rastio with the meter as we discussed, then see where we go from there. May be also time for new rotor/wires (however, those parts on the 103 seem pretty bulletproof).

That car looks a lot like mine, I have the artic white with grey leather; awesome color.
The best visual thing I did to mine was replace the wheels with 16" 1992 wheels, with the 9 hole pattern. I'm actually on my second set from Tirerack, about $120 apiece, cheaper than repainting the old ones.

DG

Actually, those are the plugs that were in the car when I bought it...I have no idea how long they were in there for...probably over 10k miles. I'm already planning for a valve stem replacement LOL.

Alright S-Class Guru..I went out and got the meter...here are the results...





The number stayed exactly the same at all times... whether at idle or 2500 RPM. I'm assuming this means I have issues...