i got this ls motor it keeps jumping from 1000 to 2000 rpms when its cold..and it does it a lil less when its warm..i want to know wat i can do to fix it..and i think the owner before changed the throttle to a gsr but i change back to an ls..some people tell me its the theartmostat..well im not sure watr it is..if any of u guys know please let me know asap its getting really anoying..thanks...

 

Sounds like a vacum leak. If ya don't find a loose vacum line or something...Take a can of wd-40 or brake parts cleaner and spray around areas that make an intake seal and listen for an idle fluctuation.

 

ima go look at dat 2moro..if not do u have any idea wat else can it be...?

 

if not vaccuum leak then its either ur iac, or the fast idle. the iac should b on the underside of ur intake manifold. the fast idle is on the back of the tb. make sure both are cleaned out n everything is there. if this isnt it then try re setting ur ecu. does the problem persist when the car is warm? does it keep gettin worse (does it keep jumpin higher n higher?) i had the problem on my ls n it turned out to b the fast idle.