running open downpipe, getting idle surge

[Boosted_out]

Well I am getting my 3 inch exhaust made up on tuesday so for now I installed my O2 housing with dump tube and my Megan 3" DP. While I was at it I also installed an EVOIII mani I had and fixed some stripped head studs with a Helicoil.
I also had to trim down my lower IC pipe to make room for the dump tube. I put the car back together and double checked everything, when I started her up the idle was fine and the vaccum was normal but after a minute or two the idle began to climb all the way to 2500 then began to surge between 2200 and 2500.

I never had any problems with Idle surge before this. I know I have a small boost leak at my TB but like I said it never made it surge before the open DP.
Ive been searching but havent found anything yet. What could it be?

Thanks Kyle

 

[Dsmj89]

Replace you TB gaskets. Also your BISS screw might be worn, i would go ahead and get a new BISS screw and cap while you're at it. Clean your IAC sensor also.
And finally, check to see if your thermostat isn't stuck.

 

[Boosted_out]

Yeah I got the new TB gaskets which Im about to throw in, and I the BISS screw is fine but I might as well do that.

But the thermostat might be stuck open cause rad fluid was pooring into my overflow tank after I shut her down.
Thanks I will go check that out.+

 

[joyfil2001]

Yeah I got the new TB gaskets which Im about to throw in, and I the BISS screw is fine but I might as well do that.

But the thermostat might be stuck open cause rad fluid was pooring into my overflow tank after I shut her down.
Thanks I will go check that out.+

Not sure if they are the same, but I have an extra 2g thermostat laying around.

 

[Boosted_out]

So it was the ISC or IAC sensor. It was really gunked up. Cleaned it and my TB, and got no more surge.

Thanks Kyle

 

[LARRY01Z28]

where cna you get a new biss screw and how does a stuck thermostat make it idle surge?? thanks larry