Why would you want to bypass it? If you had no IACV, you would have no cold start fast idle, so starting your engine would be like having an engine with a bad choke. It also raises the engine RPM to compensate for engine loads, like power steering loads and such, so the engine doesn't bog down or stall.
First let me say that I don't know everything, that's why I ask questions.
But I think you are incorrect on a couple of items. The cold start idle is controlled by the Fast Idle Cam. For engine loads it has the High Idle Solenoid. I have experienced that these components do function when the IACV is disconnected. What I think the IACV is used for is to control minor air flow changes to maintain a reliable idle. For instance, changing gears, slowing to a stop, and probably EVAP, at least on the 2.4L. If this is true, then I think I could live without it. But before doing anything rash, I thought I would see if there were some "IACV" experts in the neighborhood.
As for why I asked in the first place, my IACV is "sticking" open sometimes causing a very high idle. And no, its not dirty or otherwise bad. I have another brand new Hitachi IACV with the same effect. I think I am looking at an ECU problem where it is sending the wrong voltage to the IACV. But I haven't looked into that yet. So in lieu of a replacement ECU I thought, do I really need the IACV in the first place?
My answer was "generally speaking," not specific to the KA24DE. The IACV is different depending on the year/model/engine. On yours, it is used as you suggest, to maintain idle under loads. The ECM has a target idle speed which it maintains by varying the air flow though the IACV. Can you live without it?...probably. If you disable it, you will likely deal with a check engine light always being on, which may or may not bother you. However, if it is on all the time, you won't be able to tell when another ECM-monitored item has an issue unless it causes a drivability problem.
Just a thought: have you made sure your thermostat is not partially stuck open, causing the ECM to stay in open loop and the high idle is caused by the engine running rich? You should also make sure your fuel pressure is not excessive.
Disabling it doesn't necessarily mean disconnecting it. There are ways around the CEL, such as using a plate to simply block the airflow. But what would that do to readiness monitors? Does the ECM have other monitors that this would affect?
And you point out a couple of other items I can check, thanks.
I can't see it affecting the SRT status (readiness monitors), but I can't say that installing a plate to disable it won't prevent it from triggering a trouble code. All I can say is give it a shot and see what happens!
Hehe, I already did, even before I started this thread.
And it seemed to work fine. But as I said, I don't know everything so I wanted to tap into some expert knowledge to see if there were any other components affected. The readiness monitors were all that came to mind (I live in an emissions state), but I wanted to make sure there weren't others.
I think as long as you manually set the idle within expected parameters, the ECM thinks everything is fine. There are no "sensors" on the IACV to provide feedback.
Have you done much driving with it this way? Has your MPG been affected? While I have no direct knowledge of this particular situation, I had a Dodge Neon years ago that had a bad gear inside the transmission that was supposed to spin the vehicle speed sensor. It required dropping and opening up the transmission so I never did it. Since the car was a manual transmission, I was able to drive it and shift it, I just had no speedometer. I would get a CEL every few months and as it was explained to me, the computer was simply using some default programming and not using vehicle speed to adjust things. So... car ran fine ( you had to blip the throttle if you came off it too quick) but MPG was always on the low end of acceptable. Did it work?
Yes. I drove the car for 2 years and the guy I sold it to drove it for 3 more years like this.
Was it ideal?
Probably not. But, weighing the pro's and cons of the repair / hassle on an older / beater car meant it was the proper decision.
I finally got back to this and did a check on the signal coming from the ECU. The signal is there, but without a scope I couldn't really tell if it was the correct wave or not. But it was oscillating so I believe the ECM is not the problem. I went back to the bypass.
However, after a few days it set a CEL for 505 IACV. I'm guessing its just a calculation by the ECU on whether the resulting idle is within the expected parameters of the signal sent by the ECU. I don't believe the ECU actually monitors the IACV directly, but I could be wrong.
In any case, a CEL is not acceptable as I live in an emissions state. So I went back in to look again. I thought maybe I would try the other IACV I have again. But when I pulled off the old IACV I just happened to spot a piece of old gasket on the throttle bottle side. That really pissed me off. Apparently it was letting air pass through.
So I cleaned it up, put the new IACV on and its working fine so far.
But I just wanted to say, the bypass does seem to work just fine. If you can live with the CEL.