ok i have a 90 crx dx with a b18a1 obd1 conversion. the thing that is happening is the car have a rev that goes from 1000 to 2000 up and down at idle. it is like it is a idle air control valve but i have replaced it. if any buddy has an idea please help.

 

Sounds like a vacuum leak to me!

Check all your vacuum lines to see if anything is disconnected. You can also pick up some fuel injection cleaner and spray it at places where vacuum might leak and if there is a change in the idle it's probable that the leak (or one part of it) is coming from that area.

In my case it was a dead pcv valve. I figured this out by pinching the pcv hose between the IM and the valve shut and the jumping idle went away.