legacycentral bbs

My 91SS recently developed an idle issue that is obviously a vacuum leak (as you can hear the air leak even from inside the car... ). Well I finally got around to looking at it today and found that if I seal the hole in that port on top of the throttle body with my finger, it idles great, but when I let go, it idles low then dies.

So is this port supposed to be open or is there something that seals it off normally (I could swear I remember some kind of block off plate inside with a c-clip securing it, but am not 100% sure). The "port" I'm referring to is circled in the pic below (thanks to legacy92ej22t for the source image ). Also, it appears to be threaded on the inside, so something has to go there.

Never mind, it's fixed now!

I was removing the bracket for that plastic cover thing (which has been in my trunk for months anyway... ) and bumped the screw that was sitting beside the TPS sensor and it moved. I found this odd as I had left this screw alone thinking it was an adjustment screw like the one on the other side of the throttle body. So I pick it up and what do you know...a tapered end that perfectly matches the taper inside the port on top of the throttle body. Finish removing the bracket, insert and tighten the screw, fire her up and smoooooth idle!

Of course, this begs the question...why does this port even exist in the first place!?

Actually....that screw is a bypass screw. It allows air around the throttle plate. Works exactly the same way as a needle valve does on a carburater.

I had a high idle issue. I cleaned the throttle body, which removed this sealling goo. The TB was benchflowed and adjusted with that screw to flow a certain amount at idle. When i removed the sealing goo, I changed things. I hunted and hunted until I removed the black mount for the plastic cover. It showed that damn screw. I screwed it in a little....idle came back down.

The thing is, from like 92 on.....the TB's don't have that screw. The only thing I can think of is that the 90-91 MT IAC valve didn't have the range that the AT IAC valve did, so they had to get to fine tune the TB's a little more so idle would be correct. They used that screw to do it. In 92, when they changed all models to the rotary IAC, they did away with the needle valve.

I may be totally wrong, but that's the only thing I can think of.

here's some more pics of the TB and that screw.
http://www.main.experiencetherave.com:8 ... /images/tb

Thanks that helps quite a bit. The pics are, indeed, exactly what I was referring to.

I was talking with a friend later and he brought up that it probably was an idle adjustment screw since it was tapered like that. Fortunately, the car idles perfectly fine with it screwed all the way in (though I did notice that the idle rpm seems a good bit lower than before), so I guess I don't have to worry about that adjustment for the moment.