vacuum issues

[colleps]

i have a 95 s10 w/ a 4.3 tbi. on the front of the intake manifold there is a vacuum there. i have nothing connected to it. at idle it runs real rough but when i get on it she runs like a raped date on prom night (real good). i dont know where the vacuum went previously. when i cap it it idles nice and smooth but performance goes to crap. almost feels like its choking or misfiring. im thinking it went to the old air cleaner system. i replaced that one with an after market gimmic. any thoughts or ideas would be awesome. oh yeah... when i dont have the vacuum capped there is a heavy gas smell from the exhaust.

[onthecheap]

what's happening is the computer is trying to compensate the extra air entering the cylinders with more fuel by way of the oxygen sensor. if you plug the port that is open and let it readjust every thing should return to normal.

[chuddly]

yeah try plugging it and leave it plugged for a few days...(some computers take a bit to relearn whats goin on)

[colleps]

yeah i already plugged and left it for a few weeks. but it still seems as though its choking.

[cooperjd]

is it your breather hose? do you have a similar hose on the other side connected to your pcv valve? i have a 95 4.3, cpi with a custom intake. i had a hose that was connected to my stock air intake that wouldn't fit on the new piece.. so i bought a breather filter from autozone. i didn't really notice any rough idling when i did this, and it may not even be the same hose we're talking about. maybe this'll help