I've been doing a lot of searching on the Internet, and most of my questions were answered by this site; so I became a member.

I've found a lot of information regarding the IAC circuit and how it works, and what I've found has been very helpful. I have a Vintage Air System installed and I wanted to find a way to raise my idle when it's turned on.

At first I tried to install a couple of potentiometers wired in place of the sensors to trick the PCM into thinking I had the proper evap temperature and AC pressure, but so far it hasn't worked out too well (the Vintage Air system keeps track of evap temp and pressure internally). The PCM also expects the pressure to raise once the system is engaged.

So now I'm trying to just raise the idle enough to be able to handle the increased load when the AC is on (previously the idle dropped way too low). that's how I found out about the IAC and getting additional air into the intake under idle. I've drilled out my IAC passage a little and it seemed to help a little, but I still had to crack the throttle blades to get it to idle high enough. From everything I've read I think it's better to keep the throttle blades completely closed and get any air necessary for idle to go through the IAC air passages in the intake.

So my questions are:
1. Where does the IAC get it's air from? I don't want to make the hole too big and find out that the IAC filter is clogged or not hooked up correctly. Where is this IAC filter? The throttle body is new and the passages are all clear.
2. In conjunction with my first question what are all the hose connections to the throttle body? I know the bottom two were for coolant, and I bypassed the throttle body on my setup, but what about the other two on the passenger side? I have the lower one capped and the upper one connected with a hose to the valve cover. I have the FSM but I can't find any detailed information about the throttle body and its components.

 

The A/C request wire at the PCM is supposed to raise the idle when the A/C comes on. The wire is B1 on the black PCM connecter. This wire hooks to the A/C head unit to a wire that is hot when the A/C is on. The lower hose is for the A.I.R. equipment that you don't have. The IAC gets air from the area between the throttle bores. The lower hole goes straight to the IAC housing. If you have an airfoil it can partially block the air to the IAC. I have no clue on the filter.

 

B1 is the AC request connector, but my understanding is that it will not raise the idle unless cetain other criteria are met. The two items that are a problem for me are the AC pressure and evaporator temperature. My aftermarket AC system will not give me the outputs to feed into the PCM.

This is why I'm trying to raise the idle at all times.

 

I don't have the pressure sensor either. I was having a similiar problem until I hooked up the request wire. The pressure switch is for the A/C relay. The pressure must be at a cerain pressure before the relay will engage the clutch.

 

I've hooked up the B1 request and the idle didn't increase and it eventually threw a couple of codes (69, 71, and 66 IIRC; but this is with the potentiometers wired in place of the sensors). You got your idle to increase just by powering th B1 connector? If so, maybe there's a setting I need to change with TunerCat?

 

I am going to wire the A/C clutch status so my PCM knows the A/C is on. I had all the A/C codes turned off. I am eventually going to wire up the sensor so I can monitor A/C line pressure with a scantool.

 

I found this diagram of an IAC circuit on shbox.com
http://shbox.com/1/iac2.jpg

If this is correct, this may confirm how I think the IAC works. Somewhere in the throttle body a small amount of airflow is diverted to the IAC. The amount of air that makes it through the IAC is determine by how much the pintel is open. The air that flows through the hole between the throttle blades is not restricted by the throttle body IAC circuit(the same amount of air will flow through regardless of the pintel setting in the IAC controller); but it will use the special IAC passages in the intake manifold.

Now, I still haven't found where the air actually enters and leaves the IAC circuit in the throttle body and I've had it apart a couple of times. Maybe someone can tell me where these passages are?

This is why I think the hole between the throttle blades should be made larger and that the throttle blades should not be cracked (and I definitely don't think drilling holes in the throttle blades would be a good idea). Of course this is on engines that have high IAC counts and need more air at idle. If your engine needs more air at idle, I think it's far better to get the extra air through the passages in the intake used by the IAC than just to put extra air through the throttle blades (better distribution to all cylinders).

Please let me know if I'm correct in my theory or not.

 

Surely someone can confirm or correct what I wrote in my post on the IAC circuit?

 

I found the IAC Circuit inlet and outlet passages built into the throttle body, and determined that the IAC valve doesn't appear to be working. I removed it from the throttle body and could not get it to move when cycling the ignition. I've got a new one on order and I'll see if that helps maintain a better idle.

 

I didn't get too much help here, but I'll post my findings in case someone has the same problem I did and finds this thread.

I was seriously looking at performing the 'drill mod' (increasing the size of the 'bleed hole' between the butterfiles on the throttle body) to increase the amount of air allowed in during idle. It seemed like the right thing to do based on my IAC counts and the systems inability to keep up the idle speed when extra load was placed on the system. Luckily someone mentioned that the IAC valve was probably the problem. I pulled the valve and cycled the ignition a few times, and sure enough it wouldn't move.

I bought a replacement IAC valve and checked to make sure it would move when I cycled the ignition, and it did. I completed the installation and ensured that the butterflies were adjusted to be completely shut at idle. It started right up and kept a good steady idle. I turned on the AC and after a momentary drop in idle the IAC valve was able to adjust and bring the idle very close to where it was before the load was added. This is exactly what I was looking for.

So, I guess the lesson learned is to check your IAC valve for proper operation before resorting to the 'drill mod'.

 

So is this the best way to check the IAC? If I pull it from the TB and turn the ignition on I should see or hear it move? Can I tell if it works properly by watching the counts? What should the counts be if it works correctly?

Thankz