My 2000 Volvo S40 recently started stalling.  It appears to be caused by the vacuum leak created by whatever is now missing from the end of the cylinder head, covering the end of the camshaft.

Whatever it was, there were two screws holding it on.  I don't think it was a sensor because I don't see any mystery wires anywhere.  I don't see how the screws could have fallen out, nor can I see how the item in question could have gone anywhere but to get caught in the bird nest of hoses, tubes, wires, etc. surrounding the location.

I have tried searching for "cam/head plug", "cam/head seal", "cam position sensor" with no luck.  Any ideas what this was?

Thank you,

Joe

There is also a steel retainer plate. Some have an aluminum cap with bolt holes some had a rubber over steel plug with a separate plate with the two holes. I think the difference was turbo vs non turbo.

Thank you all!