Sudden bad idle

I took my truck in to get a flat fixed last night and today i almost get to school and the idle gets really bad and almost stalls. The car is now struggling to idle and I have to give it some gas to start. I looked under the hood and found a 6 inch l shaped vaccuum line just sitting in the engine bay. I think the shop I took it to last night could have done this. Does anyone have any advice for me as where to look to put this line back or the idle problem. Thanks a lot in advance.

1995 Blazer 2Dr

A year might help! maybe a photo?

The older years had a vacuum ball that the vacuum hose would fall off. The ball was mounted to the hood on the drivers side

Its a 1995 2dr....I will go check the ball and see if that could be where its from.

edit...it is not from the vacuum ball on the hood.

here is a picture of the hose....

pcv valve (on the valve cover) to the intake hose?

Look for the under hood vacuum line chart.
Take a good look at all the vacuum lines.

I find it rather odd that it ran well enough to get you out of the garage then suddenly started idling bad. You should be able to find the open fitting where this hose belongs by looking real close. You can also try spraying something like WD-40 on and around the top of the engine while it is running, If the vacuum port is sucking air, the WD-40 might make the engine stumble a little or you might actually see it suck it in.

I am not sure if the car shop just left the hose in my car by accident but I opened my gas cap and closed it again and the bad idle went away. We will see in the future if the bad idle comes back.