Low idle and running rich

[Mitshiko]

Ok so...I JUST took my car out tonite. Its an 86.5 7MGE engine, and it was seemingly not as powerful as it should. I assumed it was from my BHG. I just got it for 500 dollars, and I knew it had a blown head. I went to test it out, after getting the car in my name, and insured, that I should test it a bit more. I took my girlfriend home, and it was running ok. when I got back home, I went to check email, do whatever, and went to go to my aunts just a few blocks down. and...it kept dying. The engine wont hold RPM unless I rev it high, and then kinda...its not knocking, but its clunking. I hear a hissing from the back of the engine. I called the previous owner, and he told me that, Yes, he heard it too, and he and his buddy both couldnt figure it out. I have this hose, kinda "S" shaped, that I found sitting between the radiator, and frame under the hood. it has a little clamp on the end, so i know it goes somewhere. I also know with the BHG i had in my 89, that didnt affect the idle all that much, at least not enough to kill it. there is just coolant going out the exhaust chamber at times, and its not even a serious leak.

I know that when I ran seafoam through my 89, i had to pull off a vaccum line, and pour it in, which made the engine do the same thing, and make the same hissing noise.

What I would like to know, and hopefully fix, is where the hose goes, or whats loose. I cant see anything, but its also dark out, and I am not sure what is hissing, or sucking...

I read on another forum, (Supramania) that something like what im going through happened because of a vaccum leak, and something called the ISC. Im sorry to say I dont know what that is, and any help would be awesome. Pictures would help too...