Hey i got this civic si with a b18c swap a few weeks ago and all has been good until today when i noticed the idle jumped to 1500rpms. I don't know what happed or why it is at 1500 and not 800ish like normal. What could be the problem. The car drives fine other than that.

 

Try cleaning your iacv

 

Would the iacv seem like something that would cause this problem to come up so suddenly without any early symptoms of the idle slowly increase over time?

 

Could be. Id also check your throttle cable,tb plate, and check for vacuum leaks