I recently installed a Ls-vtec engine into my 93 civic coupe. Since the install the engine has been idling at 2,500 rpm once it fully warms up. When the engine is cold it idles at normal speed and as it warms up the idle keeps increasing until it reaches 2,500 rpm. This is what I've tried.

Checked for ecu codes, there aren't any.

Replaced the IACV, throttle body (with all sensors), ECT and AIT sensors with the ones from my B18B engine I previously had installed on the car (all worked fine) and then reset the ecu.

Checked for vacuum line and intake manifold gasket leaks and couldn't find any.

Tried another ecu with no success.

Unplugged the IACV while the car was running and it dropped the idle from 2,500 to 2,000 rpm, not sure if this means anything.

And now I'm clueless and don't know where to go from here.. any suggestions would be greatly appreciated. The only thing I'm thinking about trying at this point is going to purchase another IACV because maybe somehow the one from my old engine went bad.

 

check your iac valve, make sure the flapper isnt froze, also check to make sure your throttle is completely shut at idle, possibly your throttle cable is too tight, leaving the throttle flap slightly in the open position. you can confirm this by the engine idling with the throttle linkage unhooked.

 

Thanks.. I've already tried both with no success.

 

Disclaimer: I have no idea which throttle body comes with any of the b series motors, so this may not pertain to you....

But at least on mine if you take off your intake you will see there is two smaller holes to the side one for the fitv and one for the iacv... which one is sucking in air? If you cover the one that goes to the iacv it should die or almost die. Once warmed up the fitv should close (does it even have a fitv, I know some don't, sorry). If the fitv is not closing all the way, this is your problem, search for how to clean it.

 

I checked what you said to today, the lower fitv hole was sucking in air after the engine had already warmed up and when I plugged it the engine stalled because my throttle body has been closed at idle to keep the idle as low as possible. So I'm guessing my fitv is stuck open so I'm going to clean it later to see if it fixes it or replace it if I have to. It's odd that this happened because I had the same throttle body on my b18b I had installed previously and it worked fine. But anyways thanks for your help.