Why is there a rubber hose from the fuel rail to the air intake tube on a 2001 Jetta 2.0L engine? What iOS it supposed to do?

When trying to troubleshoot a starting problem on a
2001 Jetta 2.0L engine, I disconnected the air
intake tube from the air filter housing and it still
didn't start, but when I covered the hole where the
fuel rail hose meets the air intake tube, I felt suction
there and the engine started immediately. After
running a few minutes, I turned it he engine off and
let it sit a couple of minutes and cranked it again
and it started immediately without covering the
hole. I've never seen such an interconnection before
and don't clearly understand it's purpose. Blocking
it while the engine is running has no apparent effect,
but with it unblocked, the engine wouldn't start, no
matter how much we cranked it. It seems to be
totally worthless. I'm thinking of removing the hose
and capping off the fuel rail end and the nipple at
the fuel intake tube. What effects might that cause,
other than making it start easier? Also, it is winter
and I wonder if that may be part of the cause of the
failure to start, so we're letting it cool off for an hour
before we try starting it again.