E420 Engine Surging
 

Anyone have an idea why my idle has dropped (500 rpm) and engine surges occassionally on my E420??

vacuum leak?

bad mass air sensor?

Where is the air mass sensor located and how can it be changed and/or diagnosed??

The mass air sensor is located in the big, fat plastic tube that is located between the box that holds your air filter and the intake manifold.

It is held in by simple hose clamps, and takes 10 minutes to replace.

Is it that small thing near the head light in the air intake hose on the left side of the car???? Need more detail as to wear it is?

Allan,
The small thing in the left side air tube is the ambient air temperature sensor.

On our M119 engines, I believe the air mass sensor is actually in the throttle body. If you take off the air cleaner you'll see a thin platinum wire in the throttle bore which is the air sensor.

Have you tried some Techron and a good old fashioned Italian tune up?

What the heck is an Italian tune up...LOL????

If I replace the sensor is there anything that needs to be reset to tell the computer/sensors it's been fixed?

Ah, yes, the famed Italian tune up. There was recently a thread about whether this term is an affectionate reference to a time-honored tradition, or an insult. I hope it's the former.

In any event, many, many died in the wool MB fans have told me that these engines really benefit from some occasional flogging. The idea is to find a safe, hilly area and once a week or so give your engine a couple of wide open throttle (WOT) experiences for several seconds. You'll see the tach go to redline (6000 RPM) and you'll almost lose your nerve, but be strong and persevere, and good things will come. If you have carbon buildup, the first couple times you do this you'll think you've ruined your engine since it will buck and snort when it hits about 5500 RPM. But, again, be strong, keep it up, and before you know it, she'll be purring like a kitten. This did happen to me, but fortunately Stu Ritter had said what I just said about not getting shook up about the bucking and snorting ...

Some have even reported transient electrical glitches seem to improve after an ITU!

I just found this thread.

My E420 will also occasionally surge in rpm's. Mostly when almost comming to a full stop, it will surge for about 1 second.

Could that be the mass air sensor?

Craig

Let me know if you find out why yours is surging. I have the same car same year and have the same problem. I just replaced the wiring harness as these were a source of problems for our E420's. Having done that (and after $700.00) it is still surging. What is very strange is there are no error code showing up so myself AND my machanic are both stumped. ANYONE EXPERIENCED THIS BEFORE?? HELP!!!

Does a E420 have the resistor ends on the coil wires like my E320? I had low idle/surging problems and changing the resistor ends cured the problem. That and assuring the plugs were the correct, non-resistor Bosch's.

Great question!! I don't know. Does anyone in here know?

I don't know why, I was thinking of that air mass sensor. I've only had my E for 1 1/2 years. I bought it from a MB dealer and they replaced the wiring harness, plugs, caps, etc. A total of $3200 in work. Doesn't do it all the time, just every once and a while.

Craig