bmac002

I was getting a quick vibration at idle but not in park and I took it to the dealer. They said they could not duplicate the problem and now the problem seems to have resolved itself. It has never happened since I got the car back and it used to happen all of the time. Especially if the car was at a small angle where the front end was higher than the rear but not always. When they said they could not duplicate the problem when I arrived I asked to have someone ride with me because it almost always happens but I could not demonstrate and it has never happened again. Could they have done something and not told me about it? That would not make any sense because the car is still in warranty (but not for long). I noticed that my airbox was installed funny and I was not the one to do it. One of the little feet was crammed between the rubber gasket and the metal making it very hard to remove. I know I did not install the air box wrong because I took out my K&N before going to the dealer and replaced with the factory air filter so that there was no way they could say it had anything to do with the K&H? Please advise. Sorry for the long post. I have read that some dealers were replacing the belt tensioner and correcting the odd twitch that the engine has at idle and in park but this was only at idle. I have the updated control module already. The reason I ask about the tensioner is because I think it would make sense that at idle (slower idle than in park) it happened. When you put it in park it went away (like the belt moving faster had been tightened correctly). I am no mechanic this could be way off. Is there an updated tensioner for my car and if so what is the bulletin number? Thanks!!!

mbtech208

It's probably a bad mass-airflow sensor.

patrick

...as a result of the K&N???

mbtech208

Nope, as a result of being a typical Mercedes-Benz mass-airflow sensor

MercManiac

mbtech 208....does the mas show up as bad on the laptop diagnostics????

mbtech208

Usually, yes. The self-adaptation (fuel trim) readings will be pegged at the maximum limit. But if this is the case, your check engine light will also come on. It may be just starting to go bad.

patrick

self-adaption to max, check engine light,...in this situation fault codes will be in memory so there cannot be any doubt.
This will not be the case when the air flow sensor just measures a bit less air than really passes. You will feel that there is less power, but there will not be any fault codes memorised or warning lights on.
This can only be measured by making a test drive with the computer attached and measuring the air that passes the sensor at a certain RPM and accelerator to max.