I have a 93 civic with a jdm b16 swap. I recently swapped out my intake manifold and put on the AEBS Power Plus manifold. When i start it the idle surges to about 2500 then drops down to about 1500, when it warms up it surges from 1300 to 1400. for now i just unplugged the iac valve so it idles somewhat normal. I have even had the manifold off multiple times, used to different gaskets, RTV, checked to see if all of the old gasket was off, checked all of the vaccume lines, and blocked off the ports i didnt use. I dont think my head is warped but it might be. Ive tried everything and im out of ideas. Does anyone have any other ideas?

 

maybe a bad iac. sometime the tps sensor will make you idle surge. it would also make your air/fuel be off too

 

I doubt it, it was fine before I switched manifolds plus when i have the IAC plugged in, the CEL goes out.

 

Try changing you idle air control or try adjusting it because it should have a screw so you can adjust it.

 

You're head is not warped! That's for sure. Do you hear any vacuum leak, a hissing sound? Check your IAC o-ring. To make it easier, get a starting fluid from Autozone/Kragen and just spray around where possible leak is coming from and watch for idle change. You can also clean your IAC with this, clean off the carbon.
OR get a stetoscope, take off end round thing at the end and use end off the hose to listen to possible leak. It's amazing what you can hear. Good Luck.

 

Ive done what you have said with propane before, there was no idle change I even checked around the throttle body gasket and around the iac and still no change.

 

could be something else.

 

bump