Lovely E420 has CE, ASR, Limp issues
 

Undesirable Behavior
* Check Engine Light is illuminated constantly.
* ASR Light is tripped spontaneously with Limp Mode. This occurs occasionally on startup, but also occurrs every few miles at any speed.
* Engine Hesitation at low RPM. This occurs most noticeably when engine is cold and car is just beginning to move down the street at about 10mph. If the engine is warm, no hesitation is evident.
* Slightly Rough Startup. This occurs occasionally when the engine is warm.
* 3-4 Attempts To Start Engine. This is necessary if the engine has not been started for 5+ days. If the engine is not started for 15+ days, then it may require 10-20 attempts before it kicks over and starts.
* Very Rough Idle On Startup. This always occurs if the engine has not been started for 5+ days. It takes about 1-2 minutes to smooth out. The longer the engine goes without being started, the rougher the idle will be after it starts.
* Soft Backfire On Startup. This frequently occurs when the engine is cold, but is not loud and not easily audible.
* Uncombusted Gas Smell On Startup. This always occurs if the engine has not been started for 5+ days.
* Anemic Acceleration. This is most evident in the lower RPM ranges < 2,000rpm.
* Miserable MPG. The MPG has deteriorated significantly.

Parts Replaced
Recently replaced parts in this 94 E420 include:
Engine Wiring Harness
Spark Plugs
Caps & Rotors
Fuel Filter
Fuel Injection Temp Sensor Switch
Brake Lamp Switch
Neutral Safety Switch
Mass Air Flow Sensor
Battery
Valve Cover Gaskets
Oiler Tubes
Oil (with Valvoline 20W-50 Synthetic)

Note: Her Vacuum Pressure has tested fine. The MBZ Doctor has also checked the codes several times and is sure the problem with this 94 E420 is a bad ETA.

Possible Part Failures
I believe the problem(s), beginning with the most likely, may be as follows:
1) ETA (Electronic Throttle Actuator)
2) Fuel Injectors
3) Alternator
4) Alternator Wiring Harness
5) Oxygen Sensor
6) Cam position sensor
7) Wheel Speed Sensors {may need cleaning}

Questions
Would a bad ETA also cause the suspicious uncombusted gas smell (if engine sits for a week or so) on startup and accompanying rough idle?
Would a bad ETA cause terrible gas mileage?
Or alternatively, IS THIS AN INDICATION OF A FUEL INJECTOR LEAK causing a wet cylinder to develop when the car is not in use?

Over
DC

ASR cars are taken over by the devil at about that age and it's very hard to get them back. In spite of all the things you've replaced there's still a lot of things to go. It's mind boggling really how many things can go wrong on these cars. I think before you throw more parts at it you should learn how to read and erase codes. This will allow you to take a little more scientific approach. You can get the injectors cleaned and tested for about $8 each - which should allow you take that off the list. The other thing I would add, unfortunately, is that you can't really assume that the new parts you've put on there are all good. You've got to keep an open mind to the possibility of a failure there too.

A bad ETA or shorted wiring in the ETA could certainly contribute if not cause the problems you're having. You may want to read my write-up for the ETA on my S600. True, our cars are different, but the basic problem is the same...

http://v12uberalles.com/throttle_actuator_rewire.htm

You really should start by checking the codes. Here are a couple links that should get you started.

code reader tool

code list

After you read the codes, clear them, drive a bit, and read them again. It's not unusual to get spurious codes the first time you read them. Clearing the codes ensures that only the meaningful codes come back.

Wow!! Talk about the devil. . . you've got him and his army! Get a gun! :rifle:

You have gotten some good info;
1) Pete's page is great for the pics of 'crumbled' wires inside of the ETA. I would agree "sight-unseen" that the ETA has got to go. But you need to check my page, MENU#24 for symptoms of a "V8" not a "V12". You will see the codes that were set in the various key modules. And some scenarios that match what's happening to you.

2) I'd check the FP regulator; it's mostly likely leaking badly. Do a search and you find some recent posts about the hard-starting, poor idling problem.

3) Not sure I take the injectors out until you do the FP reg. If still a problem, then have at them. But remember you need all new supporting gaskets, seals, etc. otherwise they will give you a lot of problems.

4) As far as the codes, you can use my page since they are identical b/c your car is an "LH" as is mine. Also you should have the built-in push button and switch (X11/21s1; MENU#2) combo so you can read codes from the Diag Module (Menu#6). But you will need to read the other modules. There's a neat schematic in MENU#2 at the bottom of the page. Build it and use it to read codes from the other key ECUs. Or better still, maybe your tech has a scan-tool that you can use to read codes complete with detailed MB explanations. That would be best, b/c I think that you may have a bad ECU as well. Remember when the wiring harness gets real 'bad', it usually causes damage to an ECU b/c of the shorting wires. If you can narrow it down, then possibly finding a 'sub' from a working car to check. You can buy "used" ECUs from the PartTrackers Network in the Links section of my page.

You've got the MOST problems that I've ever seen in one car!!! Lot's of good luck . . :)

Got your message, I'll dwell on it. "Dead Throttle" issue sure sounds like the actuator to me too, but if anything the mileage would be GREAT because the throttle won't open fully, or course this is only intermittent. Wouldn't cause a fuel smell.
Check type of sparkplug, make sure they are the correct Bosch plug MB specs for the engine.
Popping/backfiring makes me wonder about the cam advance system, this would most likely be a mechanical fault, not electrical since you say the harness has been replaced. I'd definitely check out the possiblity of an electrcal fault, simple as disconnecting the solenoid and trying to start it.
For fuel injector leak, just check the condition of the plugs!
What does the MB Dr say about the codes? Would seem this should be the first step. Unless all this work wasn't initiated by the MB Dr, I'd say you need "a second opinion" because he is shotgunning this problem to death. If the guy doesn't know what to do, he shouldn't do anything. Sounds like a supreme parts replacer.
Gilly

To start with, you need a technician that has a scanner that CAN read LIVE data & codes from the EA/CC/ISC computer (1 computer).

MOST EA problems on the 1992-95 cars stem from the throttle actuator. HOWEVER power supply can be a real problem as well. OVER-charging has caused many problems with the EA.

Think that the fuel pressure regulator IS a good starting place on the starting problem. ON the part look for 000-078-15-89. IF you see that number get a new one 000-078-18-89!

Read my post...
 

Dave, please take a moment to read my post. My E420 does not have ASR; however, maybe my post can help. Good luck on finding the solution.

http://www.peachparts.com/shopforum/showthread.php?t=123795