I've got a 94 E320 and I am trying to chase down an intermittent (warm motor) idle surge problem that began yesterday.

Here are the fault codes:

DM (built-in) Code 4 - Air inj. sys. faulty hot film mass air flow sensor with hot wire (I've had this for months)

PIN 8 Code 13 O2S (Lambda) control sys. operating at rich or lean limit

PIN 14 Code 14 Closed throttle position contact switch.
Code 5 Stop lamp switch (stop lamp works though)


Some notes: The problem began yesterday. It's been pretty dusty and cold here in the northeast, I've yet to clean the throttle linkage. I'm confused by the Code 4 from the DM (built-in), Is it 1. the Air Inj. sys. OR 2, the MAF sensor? I've had that code for a while. Past posts on the subject call for a replacement of the MAF with some success, so I'm looking for some opinions before a MAF becomes birthday present for myself, whether I really need it or not

Any thoughts?

Thanks
Geoff

First simple check is to look at the white plastic vac line crossing from engine intake over the front of engine to the SOVs on the passenger , front side
[ under front cover]
This is vac feed for the Air pump Switch Over Valve. They crack/break and we replace them with full length rubber.
This will not only stop AIR system flow, but also bring up lean codes..
Also, verify AIR pump activation at colds start....

Thanks Arthur, all vac lines relating to the AIR and EGR sys from Intake Manifold base to Engine front to respective components checked out well.

I was confused with the combonation of AIR and MAF in the description of fault 4 on the ODB check, not sure why they mention both components with one code.

Anyway, I'm going to inspect, clean and lube the throttle linkage tonight and see where things stand.

Thanks

AIR and MAF use same 02 sens feedback for diagnosis, so when a code 4 on DM comes up, they recommend going to HFM/SFI module for further specific storage. Pin #8 [ homemade tool]
That is where they separate the inputs

To explain it in simple terms, the codes that get to the DM to trip the CE light actually come FROM the other modules through a Can wiring system.. so, usually, once the CE [DM module] gets its info, it gets it LAST from the other modules fault detection . It reports these faults back to the DM when it is determined that these faults will effect Emmission Mandates..and that is what trips the CE.
So, I always go to the other modules first....cuz I know when the car is running like crap, the DM is finally going to trip the CE... but by then, there are usally so many codes being passed , that it can get confusing .
I try to get to the faulty codes from the running module systems as quick as I can to get around to some kind of sensible code registration....
By the time the CE pops , the determining faults are hiden in a mess of faults , each caused down the line by the previous one .
A simple vac leak can pop 1/2 a doz. codes by the time it gets to the DM

Here's where things stand with the issue.

I inspected the vacuum lines (AIR, EGR, Line to dash, etc.) and found a slight leak in the fuel pressure regulator. Once done, the engine ran worse, sputtering along with surging and black smoke from exhaust. I looked into the EVAP SOV and noticed that the engine ran better with the line from the manifold being plugged (I did get PIN8 code 36 before this). Also changed sparks and connectors at each coil (all sparks caked with dry soot)

So now the with the EVAP SOVplugged at vacuum and fault codes reset, here are the flash codes that surface after a 15 minute highway trip to work.

DM code 3

Pin8 Code 9 – O2S (Bef. TWC) –voltage too high circuit open or vltg implausible.
Code 13 Lambda cntrl sys at rich or lean limit.
Pin14 No Faults

Is it possible that I fixed or worked around initial vacuum leaks but my O2S got trashed in the process?

Thanks,
Geoff

Your DM DTC is built in? Is this common in 94 models. I have paid $100 to get a SRS light out. First time was when I purchased the car and it is on again because I foolishly changed a fuse without disconnecting the battery. I wonder if my 94 S350D has it built in. Any thoughts. How would I know or find out? Is it on the original MSRP sticker? I need to get it out without forking over another $100.

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)

The 94 E-class has the 16 pole connector with a push button LED light. I suspect your S-class has the 38 pin connector, which does not have the push button LED light. But you can still pull codes by building the code reader - lots of stuff in the archives on this - although it is pretty confusing at times. First step is to figure out what you have.

I know that its a 38 pole connector. I tried buildinf the code resder but it did not work. builder error probsbly. I am going to try again. Thanks for the feedback on your system..

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)

You may have had the LED wired backwards - it only works one way. 20 gauge solid copper wire works well for the pins, available unsheathed at hardware stores (picture hanging wire), then need to cover it up with electricians tape or heat shrink tubing, so the wires don't cross, about 1/2 inch bare. It should work if you do it right. I too had it not work the first time because I had the LED wired backwards.

You can test your led tool on any 12v battery by simply putting the red lead on the pos.+ post and the odd color [test probe] on the neg. The led should light if you have it wired corrcectly [ polarity wise]

I hate when this happens

I think of my post as an ER visit for my car, its bleeding badly. Someone gets in front of the Doctor (A. Dalton, MD that is) and asks, "His blood's really red! Is mine that red?" I'm still bleeding badly....Thanks [ and no offence, I just need some attention : ) ]

Yeah
It's called Thread Hijacking..

See it all the time and over time I noticed that is coupled with the never getting a "Thank You" back after replying to it.


Anyway,
Your rich conditon could be high fuel pressure or vac leak.
Do you have a Meter?

Thanks for responding Arthur.
I know these hijackers mean no harm.....I'm just a bit anxious.


I don't have a meter, I suppose this is the only way to determine high fuel pressure. I pulled the vac line from the pressure regulator, the regulator holds vacuum and is not leaking gas. If there are circumstantial evidence type alternatives to a meter, let me know..

Tonight I'm going to R&R the O2 sensor and borrow an MAF to see what happens ( I know there's no codes produced here that call for the MAF failure, but I'd figure giving it a shot)

I'll report back.

Geoff

Ok
I only mention the meter b/c there is an easy way to test the 02 sensor on HFM/SFI units

The connector is under the rug , passenger side
If the meter is hooked up to sensor output sig wire, one simply takes the vac hose off the fuel pressure regulator and watch for the meter to go rich
[ high voltage - .9v]. You put that vac hose back on and then you can test for lean reading [ low volts - .1-.2v] by simply creating a vac leak by removing a vac hose . [The one going to SOVs is fine]
All is this does is you are manually making the engine run rich/lean and seeing if the 02 sensor responds to your inputs by watching for the voltage output of the sensor to change accordingly.
It is easy to change these engine mixture inputs manually b/c the car is EFI.
If the 02 responds , you know you do not need a sesnsor.
just a quick DIYer trick.
I don't like changing any parts til I see they are not working....
Your sensor may also just be carboned up from previous rich running and just needs a high speed run down the Pike for a few in 3rd...

PS
Seeing that you changed plugs and then had a problem, make sure you tightened the clamp at the engine side of the cross over pipe . I see this happen all the time and it lets in false air that the MAF can not register...results in rich conditon beyond 02 corrcection... same goes for the air intake sensor plug