I have a b18b and whenever I start the car it revs insanely high up to 3k and fluctuates so it goes 3k-15k most of the time until it warms up. then its fine, no rough idle or anything like that. I have yet to do the CEL check but I'm thinking bad 02 sensor, exhaust or intake leak. Not sure though, any advice would be appreciated

 

Did you mean that it revs down to 1.5k? Im pretty sure its not possible for any b18b to rev up to 15,000 rpm.

 

there are a couple of reasons you car might be doing that

1. iacv-screen might be dirty
2. vaccumm leaks
3. air bubbles in the cooling system
4. fitv

 

yeah I mean 1.5k