Orvo

My car: W126 300SE, Automatic gearbox, 1987
My problem is this:
The motor (103.981/132kw) never ran even on idle, it has always had some minor fluctuations in rpm (500 to 600). Otherwise the car is driving great, at least that's what i thought. It's my first 126 so I have no comparison ... Another 126 owner has driven my car and said that it feels a little "lazy". Anyway, I drove the car for about 8000 km without having any problems.
Yesterday I took the oxygen sensor plug out while the engine was running and realized that nothing happened. The engine runs same with or without the sensor plugged in. The rubber gasket was completely worn and it literally disintegrated when I took the plug out. The sensor was very dirty, I cleaned it, but as I said, nothing happens when I plug it out. I recon the sensor is damaged, but is there a way to check this, before getting a new one. I think that the uneven idle run of the engine and somewhat high consumption (16L/100KM - city) are caused by this sensor.
Any suggestions on what I should do next or where to start in order to get this thing fixed ? I attached a photo of the plug I took out and that I believe is the oxygen sensor.
Thanks !

Orvo

UP
Any ideeas anybody ? Need to fix this asap ...

Untertürkheim

It seems that someone may have adjusted the fuel/air mixture in order to compansate for the failing O2 sensor. I would try replacing the sensor and spark plugs with some high quality ones. There is no point in trying to adjust anything when the O2 sensor is dead anyway.

Orvo

Thank you for the reply. I will replace the sparks and the spark plugs with new ones. I think I will buy a new Bosch sensor aswell, but just to make sure: is the oxygen sensor the one i've unplugged as in the photo ?
Thank you.

Untertürkheim

No, what you have in the photo looks like the air intake temperature sensor. It is cheap, so you may as well replace it if the condition was bad. I am assuming you have checked your air and fuel filters, and oil changes, etc, are up to date?

If an O2 sensor is bad, there will be a check engine light, or an O2 sensor light to let you know.

Orvo

I'm up to date with the service except the sparks, spark plugs, air filter and fuel filter - which I will replace asap. So that's not the oxygen sensor I have in the photo ? If that's the case I'm off buying a new air intake temperature sensor - if your're sure that's the one the photo ...
Thanks again for the input.

Untertürkheim

You very well may not need a new intake temp sensor. If you cleaned it well, try replacing all the regular service iteams and buying a new seal for the temp sensor, no use replacing it when there is no problem.

An O2 sensor is part of the exhaust/emissions control equipment. That looks like it is on the intake, and from what I know, that should be the temp sensor, but try buying a new seal first rather than throwing money away.

BENZITCH

The O2 sensor is in the exhaust pipe after the header yet before the cat converters. It has a eihter a 2 or 3 wired plug(2 no preheater 3 with preheater).

Orvo

Thanks for the input. Glad I asked for your opinions, because I was about to get a new O2 sensor - which I don't need. I'm getting the service up-to-date and will then see how the engine runs. Could anyone help me with getting the MB part code for the plastic part from where I extracted that plug ? It's the big black plastic thing that goes in the air filter housing. It has some broken clamps and doesen't stay very tight fixed in the air filter housing, so I'd like to change it.

Untertürkheim

That part should have a part # on it, in fact, I can almost read it in your picture.