leftyfork
New Member
Well everybody. It has been a long journey. After reading countless posts on tightening the FITV and cleaning the IAC, I have finally found a way to fine tune the idle to get that dreaded vibration out of your cockpit and steering wheel. What I have learned, is that the base idle screw in conjunction with the IAC valve are you only two idle adjustments available without interfering with air flow through the throttle plate, and subsequent throttle position sensor adjustment. As most of you know, opening the throttle body to add more air, also changes your computer's ability to keep a good idle with the IAC and fuel mixture. If anyone has found that the IAC valve doesn't either decrease or increase your idle when it is unplugged, and if when you unplug and plug the IAC back in, the motor revs slightly, your IAC is still good!!! What's wrong is, either you have your throttle plate open too far, your base idle screw open too far, or you have a vacuum leak. Or, God forbid, all three. First, get a vacuum gauge and make sure you have a steady 22Hg vacuum signal. I used the vacuum port that goes to the EGR solenoid, but you can use any of the raw idle ports in your intake, except for the one leading to your MAP sensor. If you have good vaccuum, set your base idle screw, the brass screw located at approximately 11 o'clock on the throttle body, to around 3/4 of a turn off closed. From there, take your IAC motor off the intake and get to your workbench. Through the screen you will see a spring in there. The problem with your 20 year old IAC valve is that the spring has lost enough strength that it doesn't allow enough pure air to bypass the throttle plate to maintain a smooth idle. We're going to fix that. That spring can be pushed in closer to the valve by turning the allen screw on the end. Good luck with that right? Yes. It is not metric. It is a 3/16 allen wrench by way of a hammer. So, your IAC is mounted firmly in you vise, with aluminum jaw protectors so you don't mangle your valve mounting surfaces, right? After hitting the allen wrench into the screw ALL the way, get the allen screw so you can turn it easily in and out approximately two turns both ways. Now turn it in about one turn. Put the car back together completely and start it up. Your idle should be a little higher than you remember, and your IAC is going to obey you now. Unplug the IAC, adjust your base idle screw if needed. I set my idle around 800 because the engine is tired. The base idle screw should be around 3/4 of a turn for that. Plug your IAC back in, and the idle should go up. Turn off the car, reset your computer by pulling the 10A fuse. Now for the fun part. You have total control over your IAC and with some fine turning of the allen screw, a smart guy like you is going to find the exact spot for an almost perfect idle. My idle is around 850 RPM and is pretty steady for an old engine, 165000 miles. Good Luck!!
