When to Replace the Mass Air Flow...
 

Other than a diagnostic being done by the dealership, what are the signs one usually experiences when the Mass Air Flow Senor is faulty and requires replacement in a C220? Thanks in advance.

If you do a search you will see that it will cause fuel control problems and running problems with the engine. But pulling the codes and assessing all the information is the proper way to diagnose a problem.

Are you having any problems with your vehicle?

To me having the dealership say it's bad is not one of the signs that it's bad. Too many people there trying to sell things, or that just don't know what they're doing. The sign that it's bad is the check engine light coming on, repeatedly, with accompanying fault code, or the engine running poorly with the fault code, or both.

One symptom of a bad MAS is a surging and inconsistent idle.

I had a bad AMM, but no CE light. It was not bad enough to cause the adaptation values to trigger the CEL, but enough that I could feel a degradation in performance. Others have a CEL and a going-bad AMM, but can't feel a difference.

Now, we did see evidence of the AMM going bad and used a "known good test unit" and it cleared up the slight running problem I did have.

As to what the running problems are for a going south AMM: (can have one, or many, or none)

1. Stumble when accelerating.
2. Surging idle.
3. Uneven idle.

The AMM's job is to measure the density of the incoming air charge. If it is malfunctioning, the FI system will compensate and the air/fuel ratio will not be correct, meaning you have a rich-run condition.

Do not bother cleaning it. It might work, but only for a short time. Also, those of us that had our AMM's last a long time (my original one lasted seven years 165K) seem to be ones that change the engine air filter often, and use only OE filters.

Instead of us listing the symptoms, why don't you tell us what problems you are having?

I had a slight surging problem when engine was cold, and idle seemed slightly rough at times. Very intermittent. I checked the wires going to the MAF's, and found trouble. Granted, my car is a 95 with known insulation problems. I don't know what year your vehicle is, but you may have the same problem. I'm attaching a thread for you to look at. Please note that I mistakenly refer to the MAF as the Throttle Actuator initially. Later in the thread, I do get into the Throttle Actuators as well. Rewiring these components cured my problems. Lots of luck!

http://www.mbnz.org/forums/forums/thread-view.asp?tid=1202133&start=1&fid=13