Idle surge

[ValSU85]

I am in the same situation and its driving me crazy. I have 1994 E320 with M104 engine. I checked the engine harness and it looks good i dont see the wires in cracking stage. The noticed the problem after i took a long trip. But then after a while the problem went away, now its back. Any ideas ?

[Fernandez]

Hi Valsu85!

A search in the Forum suggested checking the following areas:

-Injector "O" rings
-OVP relay (overvoltage protection relay)
-Air mass meter sensor
-Throttle body
-EGR valve
-Fuel pressure regulator

You have already checked the wiring harness and, as yo could see above, the Oxigen sensor resolved the problem in my car (M104 engine).

Let us know how you get on.

[ValSU85]

Thanks i will go through the list and check each one of these. I will keep you posted

[therealroy]

Originally Posted by Fernandez

Hi!
Idle surge was cured by new Oxigen sensor.

hi ive got this problem whats the oxigen sensor? please ,thanks.

[Fernandez]

Hi Therealroy!

The Oxigen sensor (also called Lambda sensor) lives in the exhaust system, very close to the catalytic converter and therefore very close to the exhaust manifold. This device measures the amount of oxigen in the exhaust gases. By doing this the ECU knows how the air/fuel ratio is and can adjust it accordingly. The ideal ratio is, if I remember correctly, 14.7/1 (in terms of mass, not volume). This seems to be the ideal for both combustion and catalyst efficiency and survival. The ECU then adjusts how much fuel is injected in the intake manifold by modifying the amount of time the injectors are opened.

Cars with On Board Diagnostic systems can store fault codes relating to the oxigen sensor. That is what happened in my case.

Changing the Oxigen sensor is pretty simple (although you need ramps to elevate the front of the car). Cost in my case (M104 engine) was around £100 (?around 200 US dollars) for a genuine MB part.

Don't forget to check the other possible culprits, as mentioned somewhere else in this post and tell us what finally resolves the problem.

[GDC]

How in the heck do you unplug the MAF sensor. Mine seems stuck and i am afraid ti force it.

Greg

[bigwiki]

If the oxygen sensor fails, you should get an engine check light though. I'll start with checking simple stuffs like vaccum leaks and clean the MAF.

[barry_s_u]

I pulled the diagnostic codes from my 300E M104, 3.2l. It was coming up with an indication that the mass airflow sensor was having problems. Car would barely run at all after about a minute of running. Checked codes (see one of my previous posts on how to build the code tool) and found that the Air mass Sensor code kept coming up. I bought an air mass sensor (Ebay, $70) put it in and car runs very well now. Next step is to clear the codes and make certain that the O2 sensor is OK. It was showing up on the codes, also, but may have been a result of the bad MAS.

[GDC]

barry_s_u

How did you pull the codes? I built the LED tool but can't seem to get the car into diagnostic mode. Did you use this tool? Where was each wire connected? My car is a 93 300E and I have the 16 pin rectangular diagnostic port.

Thanks
Greg

[barry_s_u]

The post with the code reader construction and use is here:
Diagnostic codes

Code reader connections are black lead (ground)to pin 1 of the 16 pin connector

Red lead +12 to pin 16 or the + battery terminal nearby

Probe or yellow lead to the pin you are pulling codes from

IGNITION SHOULD BE IN THE ON POSITION

Press switch for 2 seconds, release and count the pulses of the LED
Do it again for next code...
Do it again for next code...
Do the above until you cycle back to the first code read.
One blink means that it's working and there are no errors

To reset each code number...
After the code is read, to clear that code, press the button for 5 - 6 seconds only (not longer or shorter). If you see it pulsing a code again, you held it too long or too short. After you clear all the codes on a particular pin, try reading them again. If they are still there, try to reset again. I had trouble and was not able to reset all codes all the time.

Bottom-line... when I replaced the MAS, the code 4 did not show up anymore and neither did code 13 (O2 lambda out of range). I was correct that the MAF being messed up affected the operation and reading at the oxygen sensor which was not bad.