So just recently my IAC valve went bad on my 03 evo. Car would stall at a stop unless you gave it gas to hold the idle. I've now bought a good used IAC valve and my car will idle fine at startup. However, when I take off and come to a stop the car will always search for idle and will stall nearly all the time. I've disconnected the battery and then hooked it up and let the car idle for 5 minutes to learn the idle. Is there any other steps to get my car to idle right?

 

Did you make sure there was a good o-ring on the new IAC? Without the o-ring it won't idle right. It's not a standard one. It's very very thin and flimsy, it's very easy to tear when replacing it.

How did you test it to make sure it's good? Is this with the a/c on or off?

 

The oring was good going on, but I can check it again. The car does it with ac on or off. However at startup when the car idles, it will auto idle up with the ac on like it should. I haven't tested the IAC valve I just got, but the car wouldn't even idle at startup with the old one.

 

There isn't anything to do other than driving the car. However, it will take longer than 5 minutes to learn the idle.

 

So should I unplug the battery, hook it back up and let the car idle for at least ten minutes? Also, the car usually won't idle on its own after I unplug the battery, I've been holding the throttle manually for 30 sec - 1 min then it will idle, should I not be doing this?

 

The last time I had my battery unhooked (I don't remember what I was doing) I noticed my idle would sag at a traffic signal. This kept occurring for maybe three short trips about town and then the idle was normal. It still kept running. So, normally, all you have to do is drive. If that is not your experience either the idle control is bad or something more is wrong.

 

Well I did another ecu reset and let the car idle for 15 mins. It was still stalling on my way home from work. I looked in the shop manual and finally found where the idle adjustment screw, aka Biss screw. I noticed most people do not have to adjust theirs, but I have no idea if the previous owner/tuner messed with it. I turned it out about 1.5-2 times and the car is idling at about 850-900 Rpms. Took a quick test drive and the car idled just fine, will do more test drives and check back in. Hopefully I've fixed the problem.

 

So far so good with the biss screw adjustment. A/C idle still isn't perfect, but never drops below about 700 Rpms then goes back up to about 1k Rpms. Hopefully no further problems will pop up, thanks for the advice from everyone.

 

sw20 when you adjust the biss screw, its best to use that with a laptop with the tactrix cable, because that screw can mess with the idle more then helping, using the laptop combined with the screw is how its recommended in the service manual. So to do it proper either take it to your tuner and in a few minutes should get it better, or have someone you know with a laptop do it. good luck.

 

dastallion, the car I bought was tuned by KevinD in Dallas, TX which unfortunately is about an 8hr drive away from me. Closest tuner I've heard of is in Albq., NM and that is still about 4hrs away from me. Is there anywhere I can just get the cable and program and would be able to adjust some items, such as the IAC valve? Any info on the system would be helpful, I've only heard of Tactrix, but have no experience with it.

 

Check for vacuum and boost leaks. Thats almost always the cause of searching idles.

 

i would clean the maf too. sometimes they can cause this too.

 

Clean the IAC, throttle body, and MAF (If you're still running the MAF)

 

Yep, still running the factory MAF setup. Will get some electronic contact cleaner and clean it out next oil change. I've also got a boost leak tester, just need a compressor and then will do that to rule out any small leaks. Car is still idling pretty good minus the A/C idle which takes it a few seconds to raise to high idle, but no stalling anymore.