Maybe Vacuum leak ???

[06fourdoe]

Hi guys
about two weeks ago i noticed when i start my engine on my 06 sierra my rpms would go up to maybe 1500 and they it will come back down to 500-600rpm
and then it will go back up to 1000rpm and then come down again.
i didnt worry about it bcus it wasnt happening too often but it started to happen almost every day.
aslo when im just idle it sounds kinda weak
took it to autozone and got the codes but it was all for the o2 sensor bcus i have removed the cats converters.
the guy at autozone told me that it sounds like its a vacuum leak.
as far as mods i just have a borla exhaust with no cats thats it
any idea what this could be? thanks

 

[marc]

sounds like fuel pump

 

[Cheeny23]

my rps never spiked when my pump was going out, only bogged down into a really rough, choppy idle.

 

[Khaos]

How many miles and what year/model?

Could be the pump like Marc said

 

[06fourdoe]

its a 2006 111k miles
and yes choppy idle

- - - - - - - - - -auto merged double post- - - - - - - - - -

and not choppy enough for it to sound cammed just very low quiet sound from exhaust

 

[dillhamm]

Test your idle air control (IAC) they commonly get plugged with carbon and won't seat creating a leak. If you have access a smoke machine is a quick easy way to find any leaks, the hose for the break booster is a great spot for testing the intake manifold.