iac problem

[mikeyjd]

I have a 93 festiva. Extremely high idle.I believe i have narrowed it down to an issue with the idle air control valve.I have swapped it out with a different one with the same high idle issue remaining.I can clamp the hose on either side of the iac to achieve proper idle.If i unplug it, it idles back but runs rough.Would anyone know if their are any other sensors ect in vehicle that could send an improper signal to the iac thru the ecm?

[crazyrog17]

You have to ground a connector near the brake booster to set the idle on the computer map. I hope someone else can take this and chime in, I don't have much time to explain right now.

[htchbck]

There is an idle adjustment screw under a rubber plug on top of the throttle body. Clockwise lowers idle, counterclockwise raises idle.

[eurotiva]

There is an idle adjustment screw under a rubber plug on top of the throttle body. Clockwise lowers idle, counterclockwise raises idle.

^not to step on any toes, but that is incorrect. That is the idle mixture screw. Although it will raise and lower your idle, it will cause other effects under different driving conditions.

The idle set screw is under the throttle cable arm. It has an 8mm hex, on a small threaded piece. In the end of the threaded piece is a spot for an Allen wrench. You must first loosen the hex with a wrench, then adjust the Allen, then lock it back down with the wrench.

[mikeyjd]

Finally got my racing motor issue figured out .Bad engine wiring harness.

[FestYboy]

^not to step on any toes, but that is incorrect. That is the idle mixture screw. Although it will raise and lower your idle, it will cause other effects under different driving conditions.

The idle set screw is under the throttle cable arm. It has an 8mm hex, on a small threaded piece. In the end of the threaded piece is a spot for an Allen wrench. You must first loosen the hex with a wrench, then adjust the Allen, then lock it back down with the wrench.

Greg, gonna step on your left little toe here, that set screw you mention above is the throtle plate set screw and there's no need to EVER touch that as it maintains proper plate stop position/gap and keeps the plate from sticking in the bore (that would cause a choke out situation). and it's position is also set to maintain a point for the TPS position (TPS idle position is based on throttle plate position). the idle set screw NEXT to the throtle plate is just that, a controled air bleed (just like the IAC). the IAC only controls the idle up untill the engine reaches aprox 120*F and then the thermostatic plug is supposed to shut off compleatly and the set screw takes over base idle control.

if you've been adjusting your idle with that allen screw, you should also be moving the TPS to compensate.

[eurotiva]

^no toes squished

Im glad you clarified that. My case is different, because I don't even run a tps

[FestYboy]

density based system i take it?

[eurotiva]

density based system i take it?

Yes sir. Map only.