Hey guys, which vacuum lines are the most important? I mean where are the ones that help your 4.0 run the best?
By the way its an 88 with the 4.0, any info is greatly appreciated!

 

All of them? They all serve a purpose, and it seems the most important ones are closest to where the lines connect to the engine. Once you get away from the line along your firewall area and go down the passenger side fender area. those just lead to the vacuum ball and cruise control if you have it. search for some diagrams to see what they look like, but i guess it is hard to elaborate more without knowing your goal.

 

Well as much as I'd LOVE to do all of them, I just can't at the moment. I would just like to find the core areas of lines to replace. I have quite a few old ones that I'm sure have cracks in them, and I think that could have something to do with my rough idle.

 

I bought six feet of rubber vacuum line ($4, available in bulk at O'reilly's, NAPA, AutoZone, Pep Boys, any car parts store) and systematically replaced all of it, starting at the engine. Any place I found a chaffed or cracked hard line, I used a utility knife to cut out a small piece and coupled it with a slightly longer piece of flexy line.

I have no idea where the leaks were, in fact, I didn't even know I had a leak but when I was finished, she idled better and my HVAC baffles worked again. $4 and a couple hours is win.