Question about idle air control

[darkarrow]

is the IAC supposed to always flow air

i have a 93 mustang gt and i pulled the idle air control, and i blew through one of the holes with the accuator still attached and a large amount of air flowed through the IAC, the IAC valve is unable to seat entirely and stop all air flow, is this normal. also when i unplug the IAC when it is still in place on the car, the RPM remains constant, no drop or surge, when i plug the IAC back in, the idle is still the same, no surge no drop, i heard this is abnormal, but i need more information.

 

[SamSnyder]

I'm not sure if it is supposed to close fully when it is deactivated, or if it could possibly shut off open. Try taking the motor part off the valve part, clean the valve part with a big douche of gummout, and see if the valve part by itself will seal. The part that seals is a little ball on a stick inside there, and I work it good with some needlenose pliers when I douche, to make sure that any crud in there is pushed out. It has sort of a weak spring action to keep it closed. The real question in my mind is whether it is working right. Does your car snap back to idle cleanly? Does the idle air bypass compensate for the a/c compressor and low speed power steering loads quickly and smoothly? The real key is whether the idle is smooth, clean and steady. If it's bypassing air all the time may not be a big issue. Ford actually sells a plate that sandwiches between the valve and the intake that has bleed screws and allows air to pass all the time. It was a fix to allow factory mechanics to tweak the idle when crud buildup became an issue in high mileage cars. I run one to allow me to tweak the idle speed up or down without moving my TPS setting. But the point is that it bleeds air as part of the process, and the system is OK with that. So if your valve stays open a little, it should be OK assuming that the rest of the system is adjusted to work with it. What you're really looking for is a smooth idle under all loads.

 

[HISSIN50]

and I work it good with some needlenose pliers when I douche, to make sure that any crud in there is pushed out.

My take (which is very much in agreement with Sam):
Since there are different schools of thought on how to set the idle (some folks set the warm, no-load idle with the IAC disconnected, so in said situation, the idle should not change) and some have it set up so the IAC flow is what keeps the car idling. So without knowing exactly how the idle was set or starting over and setting it from scratch, I dont know that anyone can answer precisely.

At that point, Sam took the thoughts right out of my noggin. If you have good cold start characteristics and decent compensation for loads (A/C, etc), then it would seem the IAC is working. Some folks (me included) like having the IAC not be required for warm idle. it comes down to preference and what works with one's mods, etc.
If you have no issues, I would leave well enough alone.

Good luck.

 

[SamSnyder]

Oh, and I re-read the end of your post about pulling the plug. That is not necessarily a problem either. You may be pulling the plug when the the thing isn't doing anything. Again, the important thing is whether the car idles good. If you want to see it work, get the car good and hot, sit at idle, and load the motor up. Snap the a/c on to max with full fan; do it with the headlights on; turn the wheel back and forth to load up the power steering; do it all together. What you're looking for is whether the idle drops or gets unsteady. You want to detect if the bypass valve is compensating for these loads and keeping the idle steady. You should be able to see it work. When you switch on the a/c, does the idle drop and stay there, or does it twitch, and then stay pretty much where it started, or even jump up a 100 or so? That's the bypass valve at work. Usually, if it was not working you would get an oscillating idle when you load it up, or a feeling that the car is going to stall out. But if it runs smooth, I wouldn't worry about it, except that cleaning the valve is good practice that only improves its performance that much more. And if you're really worried about it, they can be found in the junyard for $5-$10, although the factory diagnostic also deals with the circuit leading into it, and the possibility that the little diode on the wire had blown out.