air mass sensor

Changing the MAS is a DIY job for ANYONE.

You can buy an air mass sensor on-line for $172 . Here is one source ( no connection!)(

) Even at an MB dealer, price may not be much more. The MAS is between the air filter and the engine - a black plastic cylinder about 3 or 4 in diameter with a plug on one side. It just a matter of removing a few clips, unscrewing a hose clamp, pulling the plug and the old one pops out and you install the new one. Once in place, car will adapt to data from new sensor.

Did you have the Check Engine light come on? The MAS usually causes a fault which activates the CE light. When read with an OBDII meter ( Can be done at Pep Boys, Advance etc at no cost). The code is usually P0173, P0170 or something like that. This means bad mixture, which is caused by air to fuel mixture being out of spec. MAS gets dirty and give incorrect flow readings.

Your problem could be something else. Get the OBD codes first. And maybe go to

and post results in technical section. There are some MB techs there that are helpful.

Good Luck!

My experience is similar in that I have had several air mass sensors replaced but different in that my car is an E320 CDI (diesel). After the most recent air mass sensor replacement, which cost about £100 including labour at the dealership, the car started to manifest the same old symptoms again after a very short time. These are the same symptoms you describe but with a lower rev limit, presumably because it is a diesel. I went back to the dealership and this time they reported a failure of the camshaft position sensor. This was replaced and I have had no trouble since and this was a couple of years ago now.

My conclusion is that the diagnostic system is not completely reliable.

I hope this is at least a little helpful.

snipped-for-privacy@berkshiream.com wrote:

The diagnostic system is pretty well dead on IF you do the required tests.

If you only get one bank, left or right, giving a fault code, i.e. P0170 OR P0173, THEN the air mass sensor is NOT the problem.

You need BOTH sides, either idle or part throttle, to be at fault to condemn the air mass sensor.

OR P0173, THEN the air mass

condemn the air mass sensor.

Karl,

I am sure you are right if the mass Flowmeter is really bad, but if it is just dirty (often the case) , the on-board computer keeps trying to adapt to the changing air flow signal, using the oxygen sensors output to determine if the mixture is too lean or too rich. When it gets to a pre-defined point (out of range), the CE light comes on and you get the L & R bad mixture codes.

I have initially got just one of the codes (In my case P0173). But if I keep driving the car, I will get both. Probably one O2 sensor giving slightly different out put from the other.

I have tried cleaning the Mass flow sensor using alcohol, contact cleaner, soapy water as well as in an ultrasonic bath with a detergent. I was able to drive car on old sensor for 6 months, but when problem resurfaced, I put in a new sensor. The sensors have a hot film, and small particles or oil/water droplets that get through the filter can deposit. Over time, this affects the resistance of the film and the unit measure air flow incorrectly.

These things ARE a pain! NA and Japanese cars seems much better - MBs, VWs & other Euro cars use Bosch meters. Other makes I have owned, use Hitachi which seem to be better.