son bought a 1997 c230, and when first started, there is a sound that is sort of light a rattle that seems to be coming from the very front of the engine, just in front of the oil cap.

the noise will go away when it is given a little throttle, and i noticed that after the engine was warm, sound has all but gone. engine runs smooth as a clock.

could it possible be the chain tensioner?

also, any good links where i can see some diagrams of the engine, like expoded views in case i need to do some repairs?

 

It's more than likley not a tensioner problem but ratherthe cam adjuster. See this all the time in these motors.