So I’m working on My 1996 Honda Civic DX errer code P 1509 which is the IAC. So I replaced the control module that took care of that I don’t that goes up and down. But now It idles too high just under 1100 rpm’s so will not pass smog they said it was an internal vacuum leak everything else looks good and externally. The other Eric code says valve stuck or not opening on the way for the IAC. But there’s a brand new part on there. So where do I go next? To diagnose this

 

Recheck IAC for proper operation

Check the throttle cable, sometimes if it is in the wrong position due to work done under the hood (it can make the idle run high)

 

You might also try some throttle body cleaner ,not carb cleaner ,throttle body cleaner. Could be gummed up a little