M103 lifter noise?
 

My 91 300TE with the M103 has developed a knocking noise at idle. I'm not sure what it is but I'm wondering if its possibly a sticking lifter. The noise goes away if you rev the engine and its perfectly quiet and smooth once its warmed up. I'm attaching videos of a cold and a warm idle below.


Cold engine.
https://www.youtube.com/watch?v=f7sTo6eUQKo


Warm engine. This is after a 15 minute drive.

https://www.youtube.com/watch?v=Ff1oM05i3Eg

A collapsed lifter is a simple diagnosis on the M103, just remove the valve cover and see if they have any excess free play. Give the cam lobes a good look too while you're in there......

Does sound like lifter noise however a worn out upper bushing in the belt tensioner shock can cause a similar noise. Before you go too far just take a large screwdriver and push on the bushing to see if the noise changes.