GMC Repair: 1991 sonoma, vac line, pin hole

Question
I may be buying this sonoma truck but it idles very rough it almost feels like it is missing. If you know what a distribitor cap when it has condansation in it feels like when it is running that is what i am trying to discribe. I think it is the 2.9 not the 4.7 v-6 carborated. It has alot of vacume hoses so it may even be a vacume leak. What i want to know if the belt is off and it runs all the pullys air, alt,smog,pwrster, ect, if the smog pump is not being turned when it is running could that make it run rough because of no vacume? I took off the air cleaner cover and just with doing that it would spit and sputter when i tried to start it. Then when i put the air cleaner cover back on it started right up but still ran rough. Sounds dumb i know but if all i need is a belt to make it run better then i will buy the belt, but if im not going to buy the truck i dont want to put any money into it.
Thanks for any help you may be able to give me.

Jerry

Answer
hello jerry
my self i would do a comprosen test on all the cyl first if the comprowen is good then you know u have a good motor to work with it could be a pin hole in a vac line they will have to be checked so you know . it sounds like a vac leak to me good luck with this please rate my serivice pete