While messing with the throttle body on my junk car, I noticed someting when I go from WOT to zero percent throttle. The throttle plate will close, but bounce open for a split second before fully closing again. Does that need to happen to keep the engine running, or is it something that can be corrected?

Side question relating to throttle plates: is there a good place to get 65mm brass throttle body plates, or would it have to be custom?

 

As for that opening a split second, sounds like something might be wrong. When you let off the throttle, that plate should slam shut. I wonder if you have a spring issue on the throttle plate (maybe a bit weak).

As for a brass plate, I don't know anyone that specializes in that. It would have to be custom. Be careful. I don't believe the original throttle plate a full circle design (a little oval). Plus you want it to properly close and seal. Curious, what is the interest in brass? I would be concerned that brass might be a bit soft and possibly subject to damage during use.

 

Both my 3800s do that.. Supercharged and NA.

I also have a spare throttle body in my garage that has a brass plate. Not sure about the ones one the cars at the moment tho.

 

A weak return spring was my assumption as well.

I don't know the material used or weight for the stock plates, but I'd bet a brass plate would be lighter. ZZP uses brass plates for their performance TBs. Also, the stock plate isn't completely flat, and thus will obstruct some airflow at WOT.

 

WOW! That stock plate is NOTHING like what I have seen on any of the factory throttle bodies I have worked with. Mine have a plate made of (I believe) steel, totally flat.
Take a look at this:
'04 Monte Carlo SS - L67 Throttle Body

And this:
http://crzyz28.sytes.net/mycars/2004...p_Write_Up.pdf

They are flat. Maybe they are brass looking at the pics, but definitely flat. And that is the same for the TB that came factory on my Monte and a few I tore off in the junk yards.

 

Those throttle plates are what was in both my montes when I got them. Thats really strange. Also, I found out the the bouncing I was talking about, isnt actually the throttle body, so not the springs. Its the throttle cable. If you give the throttle cable slack, or take it off completely, then go from 100 to 0 on the TB, it closes and stays closed. Any idea why the cable would cause that?

 

Its just slack that I assume is supposed to be there.. My best guess is so you dont snap (or damage another part of the throttle (line??) during full throttle).

If you pull on the throttle cable from the engine bay, it pushes the gas pedal toward the driver's seat. I put a rubber bumper over the throttle line against the gas pedal to get rid of that cause I didnt like the noise it would make letting off the gas from WOT.

I also clamped the gas pedal (the part you foot pushes) to the pedal arm so it doesnt have that pivoting motion. I think thats what was causing the noise I didnt like.