Car rpm goes up and down during idle. What could be the problem ?

 

It's known as a surging idle. It's usually cause by adjusting things that shouldn't be, removing things without replacing the proper gaskets, aka a vacuum leak or it could be a dirty IAC valve.

There are a few threads covering the surging idle issue. There are a couple good threads in the FAQ that you should look into.

• https://honda-tech.com/zerothread/1844067
• http://home.comcast.net/~em-engineering/T2T013.pdf\

And if all else fails you could try adjusting the FIT valve
• https://honda-tech.com/zerothread?id=1003988

 

It's the aicv (air idle control valve) on the intake manifold pull it and check the screen on the inside iv had this problem on both my cars it's an easy fix