What "pumps up" when I start my 2.7?

When cold starting my '08 regular cab 2wd it first idle's around 1500rpm for 20-30 seconds until I hear what sounds like something venting, similar to a blow off valve or waste gate opening on a turbo setup, and the idle then drops to ~1000rpm until the truck is fully warm, then it settles into it's normal idle.

What is the "blow off valve" sound I'm hearing? I'm guessing something related to pressurizing of the fuel tank for emission reasons, but could be all wet.

Thanks,

Trenton

 

Hi from Klamath falls! Anyways, i really dont think i've ever heard this sound you're talking about. its a sort of high pitched sound then? not just like the radiator fan running for a little while when you start the truck? Maybe the AC condenser from running the defroster on startup?.....

 

Yeah dude, mine does the same thing. Perfectly normal.

EDIT: I dont know what it is though

 

I've had the same thing happening for a while. It's not the AC because I've had it happen with the AC off and on. I just can't wrap my head around what it is.

Edit: And this is happening on my 4.0L V6

 

If you open your hood right when you start the car, you should hear a loud screeching noise. The noise stops and then you hear that "Blow off valve noise". Poke your head around and see where it is coming from. Be quick about it, because it doesn't last long.

 

I think you're hearing the air injection pump. It injects air into the exhaust manifold at start up to get the cats up and running quicker. It sits on the right inner fender, I think in front of the air box.

 

you are right it is the air injection pump and it is located in front of the air box.