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Discussion Starter · #1 · (Edited)
I hope my fellow W140 owners are staying safe and enjoying their working rides. The "limp mode" nightmare with my S420 reemerges.

A quick recap. I had just recently passed smog with no issues. Prior to this, the car would stall and misfire intermittently when the car is warm (never when it's cold or when the car is driven daily it seems). After I pass smog, I installed brand new Bremi ignition wires distributor caps and rotors (based on the recommendation of a Benz expert in my area). I checked the spark plugs and they do look like they're full of carbon build up (they're genuine Bosch with less than15K miles). The ETA unit is one of the older models with the BS biodegradable insultation, but it has been rewired with new cable and new insulation. The main harness has been replaced with updated version. Checked CKP sensor and it is working and secured in place. No issues with the fuel system (checked pressure regulator, and pump pressure and volume).
Based on pin#19 diagnostic I got the following blips, 3, 4, and 6 which translates to Lambda control inoperative, Air injection inoperative, and Idle speed control inoperative, respectively. So then I ran diagnostic on each of the pin corresponding to the areas of trouble and I got the following: pin #4, 17 and 18 blips - No CAN data transmission with EA/CC/ISC control module (N4/1) or CC/ISC control module (N4/3) and No CAN data transmission with DI control module (N1/3). Pin #7, 14 blips - Closed throttle position switch (S29/3). And lastly, pin #17, 27 blips - LH-SFI control module (N3/1) data exchange malfunction. Strangely enough, currently there are no CEL or ASR lights (and yes, the bulbs are there) on.

So, where do I look next to fix the problem or is this the beginning of the end of my W140?
 

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95 S500, 02 ML320, 97 S500
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pull your computers out, all of them, and check the pins for any corrosion, there will be 2 pins with a metal shield around them, this is the canbus communication terminals. check for moisture in the box as well, if there is your in for some fun.
 

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Discussion Starter · #3 ·
pull your computers out, all of them, and check the pins for any corrosion, there will be 2 pins with a metal shield around them, this is the canbus communication terminals. check for moisture in the box as well, if there is your in for some fun.
Thanks for your advice. So get this. I left the car in the garage for a couple of days and then decided to just fire it up and see what would happen. It fired up normal and I took it on a short trip (10 miles or so) and it was flawless. I did absolutely nothing to it (didn't even bother to clear the fault codes). I just know the current condition will be short-lived. I will check the computers the next time the car starts to show symptoms again.
 

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Discussion Starter · #4 ·
The CEL came on again with 4 DCT blinks leading me to the air injection/vacuum system. Can anyone give me any tips or point me in the right direction on how to inspect the circuits leading to the secondary air injection (especially on bank 1) and finding a potential vacuum leak? Thanks!
 

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1995 W140 S420, no auto leveling, stock basic sedan 72,000mi. VIN # WDBGA43E8SA229905
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I have the exact same car which had the limp problem. Driving me nuts for 2 months. My problem was solved by cleaning the MAF sensor, the connecting socket to it was cleaned with the same cleaner and lastly I replaced the coolant temp sensor ( the one with 4 connectors). Don't know which was the culprit but works like new now.
 

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Discussion Starter · #8 ·
Perhaps because I don’t have access to one?
In any case, I found a broken vacuum hose (it’s wrapped into one conduit with two other clear hard plastic vacuum hoses) and it’s near the secondary air injection pump. I reconnected the hose and cleared the CEL. Let’s see if this repair holds.

Why haven't you had it scanned with a professional scanner?
 
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