Name of this part?
 

1999 ML430, 192K. Can someone help me identify this part in the attached pictures? It sits on top of the 113.942 in the center of the engine, in front of the intake/exhaust manifolds and above the fan/water pump. I cannot find it marked on any diagram on EPC.net.

Also, how worried should I be about the rattling that this part makes? The rattling sounds like marbles in a tin can. I thought the sound was coming from the fan until yesterday when I took the engine cover off while replacing the PS Reservior/gasket. Then I noticed the rattling appears to be coming from this part. Any help would be appreciated. Thanks!

Looks like it could be an air pump. Does it only run when you've first started the car and it's cold?

-Jason

No, it rattles as long as the engine is running and does not stop unless the engine is shut off.

Did some more investigating and you are right Compu 85, it is the Air Pump. So on to the next question: Should I be worried about this rattling sound? Is that a sign that the air pump is about to fail?

Should run only with a cold engine.

Remove the relay in the main box for air injection, marked K28.
Most likely a bad relay!

How do you remove the air pump?
 

I keep getting a P0442 code (emissions-small leak), there is a dry rotting vacuum line that I need to replace, however this air pump is in the way and I need to remove it to get at the vacuum line. I can't see what holds this pump in place, how do you remove it?

P0 442 is about the gas cap & intergrity of the fuel tank/ charcoal cannister system.
That code is NOT about vacuum lines under the hood.

74styles,

I also notice some noise coming from the area under air pump. It's faint. I thought it's a lifter noise at first. It sounds like semi-defective bearing noise when rollers are out the holder. I can also call it marbles in a can sound. If I put long screwdriver to the engine and put my ear to the handle, the noise will be the loudest around air pump area. It seems that the noise is coming from inside the motor. Air pump only runs once in awhile, during initial engine start in the morning and when you get off the highway. It doesn't run all the time so I cannot be noise source. Maybe it's timing chain noise? I change oil and added 2 bottles of Lucas additive and I can say that my noise quited down along with lifter noise. Lifter noise during cold morning start is gone completely. Did you find a source of your noise?

Sorry for the late reply Vic, but no I have not identified the source of my noise yet. Your description of your noise fits mine though as well. Also, my noise appears to be continuous while the engine is running. When I pull up in a drive thru with the window down, I can hear the sound bouncing off of the building who's drive thru I am in. It does not increase in volume or speed when RPM's rise.

Any more news with your noise? Does anyone else have any ideas?