I have 1991 300E2.6 with 118,000 miles and it has a low metallic clatter that sounds like it is coming from inside the valve cover; I can feel the pulses when I touch the distributer housing. It only occurs at idle with the car in drive or reverse, but not in park or neutral. Idle rpm in park or neutral is around 750 and it drops to about 700 in drive or reverse. The A/C makes no difference in idle rpm. Oil pressure at idle ranges from 0.7 bar to 1.5 bar (lower pressure with lower RPM, of course). Any suggests as to possible causes????
The timing chain was changed.I use 5W30 oil.

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