When the timing chain in our 1992 300CE was weak there was a disconcerting rumbling noise at low RPM with the transmission in Neutral. I pressed our local MB service supervisor to investigate the noise. One of their experienced techs attributed the noise to the timing chain tensioner. A replacement tensioner resolved the problem.

As you probably know the timing chain tensioner has an internal spring to maintain tension on the timing chain when the engine is not running. Once the engine is started the tensioner works off oil hydraulic pressure. Apparently the faulty tensioner was not maintaining adequate oil pressure allowing the timing chain to slap against the timing chain guides.

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Fred Hoelzle