A long time ago, this TB had been opened up to 52mm. I just rebushed the shaft since I had a vacuum leak there. When reassembling, I was putting the blades back in the same place and direction they were in but noticed the clearance still around them. I have a light behind the TB in the picture to show it better. I tried moving them in all manners to no avail. Even with the throttle stop backed all the way out I have a good amount of gap still. On a SD system, is this just a vacuum leak ruining a smooth idle? Or is it normal?

I checked a maf TB and 2 LT1s to compare. The maf has just a little gap and the LT1s had no gap whatsoever, though the LT1 has a drilled hole between the blades. So the LT1 always has an amount of air bypassing the iac and throttle blades.

What's your thoughts? In 20 years of owning a thirdgen, this is the first question I didn't find already answered on the boards. Thanks!

 

If they bored them out to 52mm and are using the 48mm blades it will allow way too much air to pass, and adjusting idle may be next to impossible. Adjusting idle you have to restrict the air passing through the plates to a specific amount so that the IAC can do the rest.

My brand new BBK TB had zero play in the blades. When they closed, without idle adjusted, they were basically 100% closed.

 

It's not that important in reality since you need to set minimum idle air - that is enough air to maintain about 500 RPM idle with the IAC completely closed. So the blades are going to be slightly open anyway. As long as you can get the hot idle IAC steps to around 15-25 it doesn't make any difference at all if the blades are capable of completely closing with no gap since they will never be in that position.

GD

 

To me it looks to be way more than needed for idle, so I'd be highly concerned they wouldn't be able to get IAC to settle at 15-20

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As it stands you are gonna be cranking on the idle adjust screw, note that it affects your TPS voltage when you do that. You will need to reset your TPS during/after idle is all dialed in.

 

Yeah that's a concern for sure. But as easy as swapping the throttle body is, I would try it before I decided it wasn't going to work the way it is.

GD

 

Much appreciated guys. I'll tinker with it to get them as close as possible. They are certainly not 48mm blades. They won't come close to fitting in a 48mm tb, but it was a thought I had as well.

Also, I was under the impression SD tps zeros itself out, they aren't adjustable. Am I missing some detail?

 

Not missing anything, you are correct.

RBob.

 

I have a lot of t-bodies with gaps like that, no issues.

 

I forgot about that self zeroing tps on SD, one less rain dance you have to do