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  #1  
Old 06-27-2001, 05:31 PM
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Having searched the archives and found a similar discussion, I was hoping to request further clarification. The originator of the original discussion is graciously assisting me in figuring out this problem, but I wanted the collective wisdom of all members. My check engine light came on, although the car seems to be running well. I pulled code #19, and have seen the TSB which calls for a replacement computer, particularly in the Jacksonville area. I live in Southern California, and this has apparently always been a California vehicle.

I obtained a replacement computer from a salvage yard bearing the same part number, despite knowing that a new part number was available, since this had taken care of the problem for another member. For nine days, the check engine light stayed off, but then suddenly reappeared. Clearing the code out and shorting out the 1 and 4 connectors did not prevent the check engine light from coming back on very quickly (less than 30 minutes of driving). I am sending the computer to this other member as he was friendly enough to try it out in his car to see if we could isolate the problem to either my car or the computer. Now that I have switched back to the original computer, the light has not come back on, even though I have made many trips, some up to 90 minutes at a time. While I fully expect the check engine light to return, I was hoping for an explanation as to why it would not immediately return, as opposed to this delay.

If the computer works normally in another E420, what are some of the other causes for this behavior? I believe that error code 19 suggests a fuel injector problem, but like I said, it seems to be running well in all respects.

Finally, the idle on the car seemed to be a little lower than normal (under 500 RPM), and it would very rarely stall at a stop light. I went ahead and used Redline Fuel System Cleaner on my last tank of gas, and it is now idles at about 700 rpm. I don't know if Redline would make such a difference or if this is simply a coincidence, or if, in my boundless optimism, a previously clogged fuel injector could have caused error 19 and the check engine light problem described above. I guess my real question is what is the normal idle speed for the 94 E420, and is there any adjustment? Thanks.
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  #2  
Old 06-27-2001, 07:01 PM
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NO idle speed adjustment! However cleaning the throttle plate area with scotch-brite pad might help the idle speed to return to normal. To get rid of the check engine code(19) the modified LH ECU is the best fix.
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  #3  
Old 06-27-2001, 09:34 PM
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. . . well documented . . .

screedchan, well written report!

Have a friend whose '94 S420 does the exact same thing! He, unlike me, is not concerned now that he 'knows' that it may be the computer and not an injector. His car runs as smooth as glass.

In all of the cases I seen on this forum, it always seems to be the ECU! Be interested in the conclusion.
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  #4  
Old 06-27-2001, 09:45 PM
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Idle speed. . .

ALL-DATA CD-Rom says for engine temp 60- 80C, idle speed sb 550-750 rpm.
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  #5  
Old 06-27-2001, 10:00 PM
curiousnoe
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same problem with 400E

I have the same problem with my 400E. My check engine lights is and is idling to low at a stop. The problem with mine is that whenever I start my car, I have to keep my foot on the gas pedal to keep the engine running. Whenever I let go of the gas, the engine dies. But when I let my foot of the gas slowly and I tried to keep the idling, the engine will continue to run and I'm able to drive, but it would still idle low. Would this be a similar problem to the 94 E420?

Thanks
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  #6  
Old 06-27-2001, 10:05 PM
curiousnoe
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same problem with 400E

I have the same problem with my 400E. My check engine lights is and is idling to low at a stop. The problem with mine is that whenever I start my car, I have to keep my foot on the gas pedal to keep the engine running. Whenever I let go of the gas, the engine dies. But when I let my foot of the gas slowly and I tried to keep the idling, the engine will continue to run and I'm able to drive, but it would still idle low. Would this be a similar problem to the 94 E420?

Thanks
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  #7  
Old 06-27-2001, 11:47 PM
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MBDOC

I understand that swapping the computer is the "best" fix, but that implies that there are other fixes available. Moreover, is there an explanation as to why the check engine light does not immediately come back on when the same computer has been pulled out and returned to service some days later? Finally, what exactly is going on within the original computer which causes the check engine light to come on, and what is different about the new computer? Is this related to heat, age, milage, humidity? Why are cars in Jacksonville more prone to this problem?

Sorry for all of the questions, but inquiring minds want to know! Also, inquiring minds are loathe to spend $2000+ on a new computer. Thanks.
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  #8  
Old 06-28-2001, 10:58 AM
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. . . self adaptation

Is there an explanation as to why the check engine light does not immediately come back on when the same computer has been pulled out and returned to service some days later?

If it was the 'self adaptation' feature at its limit that caused the CE light, it takes a number of 'trips' to change to what it was. A 'trip' is defined as; 5 mins of engine operation; speed greater than 5mph and tach greater than 500rpm.

So starting the car and shutting it off is not considered as a trip. Also running the car for 90 mins is considered just one trip (assuming the other parameters were satisfied).

If an injector is bad, i would think you surely would notice it! The car should idle roughly.

So it does takes some time for this to happen but you seemed to indicate that you have satisfied the 'trip' requirement and light has not come back. Don't know why!
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  #9  
Old 06-28-2001, 05:52 PM
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I'm the one testing screedchan's new computer. When I get it, I'll run it for a few days (at most).

I'll also replace the chip with the "updated" version, as I got it from someone else who went through this same problem some time ago and replaced the ECU to the new Part# recommended by Mercedes.

Hopefully it will work.

Willy

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  #10  
Old 06-28-2001, 07:07 PM
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Since the fuel system is running *RICH* that means that the return voltage fron air mass sensor is too high!! OHMs law says that resistance can lower voltage, so yes there are other repairs! if you can figure out the return voltage from your air mass sensor to the ECU! The DM has to see the LH-ECU at that limit(.85) to turn the check engine lamp on.
CLEANING the throttle body DOES help with LOW idle speeds.
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  #11  
Old 06-29-2001, 12:22 PM
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What is causing the car too run rich to begin with? What exactly is going on with the ECU to cause this? Also, how difficult is it to remove the throttle for cleaning? Thanks.
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  #12  
Old 06-29-2001, 06:35 PM
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AS the service bulletin says the problem is in the ECU's chip program. MB screwed-up & should have recalled as many of these cars fail emission testing! At out dealer we notified our customers & installed REMAN ECU's when they were still under warranty. MB stopped with the reman/exchange units as soon as they were all out of warranty!
The throttle body can stay in the car for cleaning, only the air mass sensor & connecting rubber boot have to be removed. WE use a fine scotch-brite pad & air intake cleaner, make sure to wear rubber gloves. I always vacuum out all of the crud before starting.
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190E 2.3 16V ITS SCCA race car (sold)
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  #13  
Old 06-29-2001, 06:40 PM
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wjm, who contributed to this thread and graciously agreed to test out my replacement ECU, mentioned that he obtained the new chip from a ECU which superceded the ECU in my car. Does this mean that switching out that chip will take care of the problem, or is there another chip which controls fuel delivery? Thanks.
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  #14  
Old 06-29-2001, 09:24 PM
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'94 S500: only 793 sold!
 
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. . . MAF

. . only the air mass sensor & connecting rubber boot have to be removed. WE use a fine scotch-brite pad & air intake cleaner, make sure to wear rubber gloves. I always vacuum out all of the crud before starting.

Does this help the fault code '19', the low idle speed, or hopefully both? I think it just helps the low idle speed. The reman ECU fixes the DTC 19? Or as Willy said, the new EPROM chip?
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  #15  
Old 07-03-2001, 06:16 PM
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Like clockwork, exactly seven days after I put my original ECU back in, the check engine light came back on, again reading fault 19. I really don't understand why it would take so long to come back on, especially since I probably put 1000 miles on the car in that seven days. Now that has reared its ugly head again, I know that it will continue to come back on within 30-60 minutes after I clear the code. Can anyone explain this strange behavior? I am still holding out some faint hope that the revised chip from the newer computer will help with this problem, but who knows with something as screwy as this. If anyone has any ideas, I am all ears.
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