when i start up my car, my rpms bounce from 3000 to 1500 rpms. It does this for a few minutes. Why could it do this? I don't have an aftermarket intake btw. It's a D16z6 engine all stock

 

IACV (Idle air control valve) is going bad. Take it off the intake manifold and clean it.......check agian if you still have to problem, replace it.

 

If the engine isn't moving along with the tach's reading (i.e., the problem is isolated to the tach) , then I can almost promise you it's the ignitor, inside your distributor.

If the engine is wandering, Spade is probably right (though that seems awfully high for the IACV to be causing it)

--Karl, who has had, and fixed, both problems

 

the engine is going along with it. It still goes up to 3000 rpms when it was 40 degrees out or it was 20 degrees out. It almost sounds like the engine shuts off for a second, drops down to 1500rpms then starts again

 

IACV