i put in a skunk 2 manifold yest. on my 2000 si. the car idles at 2000 rpms, and then when it warms up it starts reving up and down between 1 and 2500 when the car is at idle and it gave me a check engine light. i had a type r ecu which i put in this morning and it took care of the check engine light, but its still has the high idle and up and down reving, there is a vacuum hose thats not connected cause i need a Y connector to run the two hoses to the valve on the back end of the manifold. could that be it? or is it something more serious? let me know asap

 

Plug that vacuum hose up and your idle will be good.

 

connect the hose and that will take care of ur vacuum leak. i hope u replaced the intake manifold gasket. good luck

 

What they said. If it still does it after you hook up the hose, than you have another vaccum leak elsewhere.