Vacuum tube left open after removal of vacuum system

[denbmd]

While cleaning plugs on my M20C, a mechanic saw this tube open off of cylinder 4. Presumably, this is a remnant following vacuum system removal. Would there have been a reason this tube was left in this state, or maybe a cap was dislodged? I was having plugs cleaned due to heavy pattern work after plane purchase and the thought that a lot of full rich flying was fouling the plugs. Yet, this finding would suggest this cylinder was likely running very lean.

[takair]

That was likely for the standby vacuum system.  Needs to be capped, or preferably removed.  Yes, would make that cylinder run lean.

[EricJ]

+1 that was probably from a Precise Flite standby vacuum system, and the intake tube has a hole in it that needs to be repaired or replaced.   I deleted such a system when I bought my airplane and found a replacement intake tube fairly inexpensively.

[bcg]

I would do like EricJ did and get a replacement intake tube.  It was standby vacuum and you definitely need to cover that up, it should not have been left that way.

[cferr59]

It is hard to believe that someone would have left it like that, but here we are...