Why did tech plug vacuum line?

[shertex]

Car I had lent my daughter had extremely poor acceleration on the lower had (noticed this when I drove the car for first time in months over Thanksgiving). Tech in VA diagnosed it as needing pressure converters/transducers for EGR and fuel mix replaced. I decided to hold off for the time being.

Got the car back, and this is what I noticed: to the left of the air filter there are two vacuum lines that merge into one. That one line is disconnected from the adjacent vacuum pod (I'm assuming that's one of the transducers that needs to be replaced...but I'm not certain) and there is a bolt (brand new) plugging up that vacuum line. And there's a short length of hose coming from that pod that's not connected to anything.

And the acceleration seems markedly improved (though not as good as it should be).

So I'm just curious: what exactly did the tech do and why? Why am I noticing improved acceleration? Is there any downside to having these lines disconnected? Whatever the reason, seems like a great stop gap measure.

Thanks.

PS When I can get ahold of the tech, I'll ask him....but figured you guys are easier to get ahold of on a Saturday morning!