Uh oh...

I was fiddling with things today (replacing fuel hoses, etc) and decided to do some cleaning in the engine compartment. While doing so, I found something that surprised me. The valve on the firewall that senses boost pressure (the line coming from the intake manifold and the line coming from the ALDA attach to it) has been bypassed. The two lines are now connected directly to each other, although I was surprised to find the ALDA line going into the banjo fitting that (what looks like) a vacuum line also goes to. I don't know how long it's been like that, but it's certainly from before I got the car.

First, how do I ensure that the valve's actually in working order? Second, what exactly can bypassing this line do? Last time I found a turbo boost line altered on a vehicle, it allowed the engine to overboost and overfuel, and irreparable (at least without completely rebuilding the engine) damage had already been done, so you can see why I'm seriously concerned about this... BTW, the line is partially cracked at the ALDA side, although that may have just happened. The car (at least I think ) drives perfectly...

Any thoughts would be appreciated. Thanks in advance!

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2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999