Hello, i have 1.6 99 civic (d16y4) engine
I just swapped the auto transmission to manuel. After doing that i've been having a high idle problem when the engine is cold. When i start the car in the morning the rpm goes up to 2000 and 2200 after few seconds.. and it wont go down untill the engine is hot..Please help!

 

unplug and remove the IACV from the intake manifold Clean it out with brake parts cleaner and re-install. Make sure to cap off the coolant lines because it will leak everywhere if you don't.

 

but why did this happen after swap? I never had a such a problem before converting to manuel.. could this be ecu related? Because im stil using the same ecu..

 

So, you left the engine in the bay and only changed the transmission right ?

 

When I converted my eg to stick, it would surge really bad when cold and even do it a little when warmed up. I swapped the resistor in my P28 ecu to get rid of the CELs for the auto trans and then it stopped doing it. I think I also adjusted the idle screw on the throttle body. I don't know if you can do that with the OBD2 ecu but if not, I would get a manual ecu for it.