ok i put the new p28 ecu in and when it gets warmed up and i hit vtec and go back to idle it bounces between 700-1200 rpms wondering what it could be. i have a 99 civic ex with a b18c5 oh and i got a v-afcII. please help

 

What do you mean bounces? It isn't uncommon when falling from high RPMs to have the RPM go a little low and then bounce back up especially with a lightened flywheel.

 

but this is at idle just sitting at a stop the rpms all of a sudden start bouncing from 700-1200 rpms and does it for about 2min then stops and idles fine.

 

i think air in the coolant will cause your idle to be like that. thats what happened to my car too after i did my swap. i fixed it by bleeding the coolant.

 

thanks man