DM DTC Code 4 Question

[104.992]

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

[Arthur Dalton]

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....

[104.992]

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

[Arthur Dalton]

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

[104.992]

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

[nhodges]

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.