300E Rough Idle and "Strange" Repair
 

Long time reader, first time poster...

I just received my 1987 300E back from a reputable independent mechanic, and I noticed a seemingly strange line on the bill. It makes no sense to me, so I thought I would ask here if this makes sense to anyone else. Here's the entry:

The engine idles rough
-Remove the Lambda tower and drill out plug.
-Install 560 Ohm resistor as per MB service information, in the 2 pole temp sensor.
-Adjust the fuel mixture for smooth idle.

The car does idle properly now (which it never has in the past).

The (quick) explanation was that the lambda adjustment alone did not do it, and so they added a resistor in series with the temperature sensor to give it a bit more fuel at low RPMs. This method was suggested by an old MB service bulletin. Adjusting the fuel mixture to give a smooth idle is not how I understand the Lambda should be set.

I searched the site for info on this and found nothing. Any clues?

DrJ

I know that when I adjusted my lambda the idle got smoother. The closer I adjusted to 50% duty cycle the better the idle got. I don't know exactly why.

Here, maybe Steve B's article will help a little...
http://www.continentalimports.com/ser_ic20134.html


Interesting info though. That makes two very interesting things to do with idle in these cars that I have learnt from this forum today... :D