S210 knocking at idle.

[chrisispringles]

About 2 years ago my dad bought a 2000 S210 E240 and all the time we have owned it there has been a loud knocking noise from under the bonnet when the engine is idling. We tried adjusting the throttle cable to change the idle revs which worked temporarily but the knock has returned. The present idle is at about 600-700 rpm and the knock doesn't happen at any other time than at idle. Anyone here got any ideas?