Ok i have a jdm h22 running a chipped p28 and whenever i plug the iacv the rpms stick at 1500 and just bounces up and down at only 1500 rpm. i disconnect the plug and it idles fine but lets say i give it gas with the iacv plug disconnected and leave it at 1500, it does the same thing, bounces up and down at just 1500rpm,it doesnt bounce at no other rpm range but 1500rpms only, i put a new iacv in and does the same thing,and i bypassed the fitv and even before that it kept doing it, any one ever had this problem thanks....oh yea lets say the car is warmed up, sumtimes i could hook up the iacv and it wouldnt do anything,idles perfect but as soon as i turn the car off and bak on with the plug still connected it goes bak to that 1500rpm bounce....

 

Is the computer showing any codes? Have you reset your idle? Sounds like it could be a possible MAP sensor issue, but check your codes first.
Later, Davey

 

the only code i get is a 14 for the iac valve, i put a new 1 in and does the same thing, how do i reset the idle??

 

Now have you reset your ECU after unplugging the IAC? Or did this code show up after the car started acting up? When did it start doing this, just all of the sudden or did it start acting funny over time? Since it's showing the IAC code (that is if it wasn't caused by you just unplugging it) then it may be an issue with the wiring. Have you checked that? I'm pretty sure you've got a 3 wire IAC and so you should have a 5 volt reference wire, ground wire, and a signal wire. So if any of these wires are shorted or grounding out then it will cause an issue.

As for resetting your idle, it's easy and even easier if you've got a Tach. Basically just unplug the IAC and then go to the 'air bleed' (or minimum air rate) screw on your throttle body and screw it in just until the car wants to die or when you idle around 550-575 rpm. Then reset your ecu and plug back in your IAC and your car should idle correctly or around 725-775 rpm.

I had a problem similar to this and it was because my throttle blade was bent from a nitrous back fire I had at the track. I didn't know this for the longest time. I kept searching for vacuum leaks and bad injectors and such, when that was all it was. I replaced the throttle body (I could have bent the blade back and been just fine, but I had an extra throttle body anyway). After doing so I set my idle and the car has been perfect ever since.
Anyway, if you can't set your idle like I described then you have another problem. Somewhere you're getting too much air and the IAC can't idle the car correctly because of it.

Good luck, let me know what you find or if you think of anything else.
Lates, Davey