It seems to be coming from the throttle body but I'm not sure. It has the same sound with the engine cover on. The car has a rough idle, the RPM needle drops and jumps back up. Sometimes it even stalls. I have cleaned the MAF sensor and the throttle body but nothing changed. The air pump seems to be working fine. Could it be a faulty MAF sensor, a vacuum leak, or an old fuel filter/pump? If not, what else could it be, and how can I diagnose and repair it?

Check your intake flap actuators and make sure no part of the linkage is broken.

I just had the same issue turned out to be I had 2 bad coils . Get a good scan tool and look at the live data . Look for a coil thats misfiring. Your looking for the cylinders that looses spark for a second . I had no check engine light on mine but when I pulled up the live data you can see 2 cylinders misfiring for a split second but it wasn't enough to throw a code .

Thanks for the reply. I did have a check engine light and the scan tool showed three codes: coil C, coil G, and misfire in cylinder 7. I replaced those two coils and the car seems to be idling smoother, but this problem still did not go away. What kind of scan tool could I get to look at that live data? I don't wanna throw the money on 6 other coils just to find that the problem is still there.

Scan soft MBII is the best for Mercedes for around $150 . Get it used and save money . Can you do this . tun the engine open the hood and take off the small front engine cover . take a long screw driver and look for plastic flap actuator on the intake . if you put the screw straight down you should be able to open the actuator . see if it goes away . If it does its the actuator inside the intake and you will need a new intake . Be careful as the engine is on . The next thing to check is the valve body . Turn on the engine and remove the engine cover and MAF . Take a mirror and look at the valve body while idling . If its moving on its own and is causing the flapping Then your valve body and or motor is going bad. You will need a new valve body . If you have a horoscope camera it will be even better . Do this before buying the scanner .