Recently I posted up here about my PCV valve and how disconnecting it made my car stop the idle surge and run normal. Well turns out that my gas cap wasn't closing all the way and that was causing the idle surge and the slight misfire. So if anyone else is experiencing any idle problems and needs one more thing to check, check the gas cap. At the top of the filler port where the gas cap screws into, there is a plunger, if you push it in, the cap will be able to close all the way.
I was wondering if anyone knows what the heck that plunger is for also.

Its designed that way, so if fuel makes its way up the filler neck while your driving, around corners, It doesn't overflow out past the port, of course a little trickle will. Though that is next where the gas cap comes into play, It finishes the seal, & holds the fuel pressure.

Jeff.

Are you talking about the metal trap door?

Yes. Otherwise there is just an overflow valve at the end of the filler neck, In tank. & It resembles nothing of a plunger IIRC.

Jeff

I am talking about that square thing above the trapped door

NEVER have seen it. Not on avengers, sebrings, or 2GNT's. I will go & look on my 96, but I know there isn't something there.

What year are you? 95?

I'll go look & see this morning.

Jeff.

I drive a 96 rs and my 95 talon has the same thing

Okay, I just looked. Yes, its there.

It seems as if that plunger gets pressed in from the outer wall of the gas cap threads. Must be some type of purge to help in ease when you remove the gas cap, so the gas & fumes can de-pressurize a little bit, instead of doing it rapidly in your face.

Thats my guess.

I'll look around though, looks to be built into the fuel filler hose.

Jeff.

I was looking at it again and if i push it in and make it get stuck, it will come back out when you push open the metal flap. This is really weird, but now my car is back to the weird idle crap again, so it is back to looking for other things for that.