i put a zc in my 89 crx si .. all sensors are plugged in and i have right ecu. coolant was bled and there are no vacuum leaks . it will idle at like 2K for the first few mins then the idle will just go up and down by itself and wont stop unless i feed gas? i replaced all sensors but still does it. even changed the throttle body. any ideas? this is very annoying//

 

try the idle control valve usually those go bad

 

that was already replaced

 

do you have a after market? have you checked the head gasket?

 

I had that similar problem with my 94 civic EX. My dad has a close friend who is a mechanic (helps for discounts) He said it was some gasket, cant quite remember what one, it was right next to the throttle control sensor. I know you said you replaced all your sensors, but check that gasket and maybe that might be the problem.