Alright guys I have searched and searched and searched here and all of the web for information on this plug/valve thing on the 03 Evo 8 only. Noone seems to really know what it is even called but it is the only point in my system that has a boost leak and it is killing my drive-ability and I am due for a tune next week.

It is directly below the TPS sensor on the firewall side of the 03 Evo, apparently some 04's and all 05's do not have this plug/spring/valve thing. It is held in with a single phillips head screw and there are two tiny plastic half moons that lock around the shaft.
I removed this plug to try and replace the o ring and stop the boost leak, simple enough right? Well it would have been but one of the half moons on the end of the shaft came off on the way out and dropped into a tiny hole that I believe feeds in into the IAC valve so I think I can get it out by pulling the IAC but I dont know how I would get them to stay in place to re-install.
Again the only information I can find anywhere on this piece is these links.

https://www.evolutionm.net/forums/ev...ame-thing.html

https://www.evolutionm.net/forums/ev...oost-test.html


Would I be able to just get a new o ring and leave both half moons off and just put the part back in the hole to seal the boost leak? I ask this because people are saying that this part is useless and isn't needed for the car to function normally.

Thanks for any and all help

 

Years ago this was a wax pellet thermostatic device that supplied more air for cold idle. Since it isn't even mentioned in the 2003 FSM it may be that Mitsubishi had some throttle body castings on hand it used up without functioning thermostat innards.

 

So does that mean that I dont need to put the pieces on the end and that I can put a new o ring on the shaft/spring part and seal up my leak or what am I gonna have to do to fix this stupid thing haha. This is an odd part for sure!

 

I keep running into problems, I tried pulling the IAC off to get out the half moon plastic piece that came off this mystery device were speaking of and the bottom bolt for the IAC is BROKE of at the head so I am gonna have some fun getting that out without breaking it if thats even where the piece dropped down into.

 

just find a used TB and be done with it.
i think i have a couple

 

So as an update I fished the other piece of the part in question out of the IAC hole.
There is no reason I see to replace this throttle body when it is in great shape and the shaft seals hold boost fine. Most used TB's will be leaking somewhere.
I just need to know if the piece in question has any crucial function or if I just need to get the hold sealed and/or how to get the two half moon pieces to stay on the shaft (if they have to go back on there) so I can reassemble it with a new o ring and hopefully be good to go.

 

Since nobody seems sure of the effect, how much trouble would it be to stick on a new o-ring without innards and see what happens. I have an '03 and I'd appreciate knowing.

 

Yea there really isnt much info out there on the issue. It wouldn't be any trouble at all I just wanted to make sure it wasn't an important piece that had to be a certain way, I just dont want to hurt the car I have too much money in it and it still needs tuned as I recently made some big changes.
Im going to give it a try though if noone else comes through to shed any light on the situation Im gonna wait for my new O ring for my IAC to come in and locate one that will work for this thermostatic flapper thing. I don't see that it could do much harm.