420SEL whirrling /humming sound
 

On the first start of the morning there is a low pitch whirling/humming sound comming (I think) from the passenger side of the engine compartment. It is easy to hear,it sounds as though it's speed is tied to rpms and it stops suddenly after a min. or so. Has anyone else had this occur?

could it be the air pump? i think that's normal...

It is the air pump, but the noise it not normal. If you can hear it than it is on its way to the junkyard. The air pump is part of the emissions control system and generally only operates the first little bit until the exhaust warms up. I had to replace the air pump on my 420SEL, and its not a cheap part. I bought a used one from an auto recycler for 1/2 the price and the an MB dealer installed it for me. Everything is working fine.

I had my air pump rebuild a month ago in California for $80 including shipping.

Thank you gentlemen.

Dennis, please let me know who did the rebuild for you as I am also in CA

Also, where is this pump and is it belt driven?

The place was http://www.moto-parts.com/ on the web or 1-800-745-1531. It was approx one week turn round.

The pump is low down below the alternator and has a electric clutch like the air conditioner. The overhaul did not include the clutch.

I have not re-installed it back on the car yet, but it was frozen solid at removal.