IAC coolant lines?

[wildncrazy]

A friend has his engine torn down and we were looking at the IAC valve and all the plumbing to it. We had trouble understanding exactly how the valve works, but by unplugging mine we can see that it does work. My car quickly threw a CEL and after seconds gave us a very rough idle even tho the car was warmed up.

Since we can't simplify things by removing the valve itself we looked at the stuff that really caused the most problems with the IAC in removing the engine - the plumbing. We were thinking things would be a lot simpler if we could remove the coolant lines. Both the IAC coolant lines and the throttle body coolant lines don't actually run thru anything, but they just touch the valve and heat by conduction.

Another change we will be making will be to run the Hondata manifold gasket that blocks off the one passageway that actually runs into the manifold.

You had this to say in another thread about the coolant line to the throttle body, does the same thing apply to the IAC?

"Remember that the throttle body is like a big venturi and air flowing through a venturi will speed up, decrease pressure and hence, cool down. There is another purpose to that coolant line. The coolant continues to the Idle Air Control system so the ECU knows when to phase out of cold fast idle. Without the coolant going through the IAC, it must heat up via convection and conduction and the ECU may take much longer to step down idle. During this time period, the A/F is much richer than normal. A few people have blocked that line on purpose thinking that it will help prevent overheating of the throttle body. A well known and trusted S2000 tech has indicated many times in the past that this is false economy. It may temporarily keep the TB cooler but convection and conduction within the engine bay will strip away that advantage very quickly. In the process, the ECU will run the engine in a way that is less efficient."

[repiv]

I'm not sure what you have in mind when you say, "does the same thing apply to the IAC", but in the sense that the coolant in that circuit warms up as the engine warms up, it does the same thing. Remember the old fashioned "heat riser valve" and the choke mechanism? This coolant does the same thing (as the heat riser), but far more effectively. The IAC mechanism regulates the amount of air that bypasses the throttle plate during cold start up and idle (like the choke). The coolant tells the sensor when it's warmed up to a designated temp and this signal tells the ECU to tell the IAC solenoid to switch itself to the position that changes that airflow.
The Hondata manifold gasket essentially blocks that coolant circuit through the throttle body and IAC system and both then warm up via conduction through the metal parts of the upper engine and via convection as the engine bay heats up. This can be far slower than by coolant actually flowing through those components. If you live in a place where the engine never sees freezing temps, no big deal as the warm up time is minimal, but for those of us who drive this car in such conditions, that coolant flow is essential.
I've often considered putting a valve on that line that could be shut off during the summer and opened up during the fall, winter and spring. Even without the coolant circuit, you still need the solenoid to regulate the air during a cold start even in the hottest summer. The first start of the day for an engine is still considered as being "cold". The ECU still goes through an enrichment cycle during those first few seconds to a minute. The IAC is involved in that.