IAC adjutment screw

Ronald Wendt

Registered User
Sorry for being so dense but..... I put on a BBK TB, it was a Mustang unit so I had to change the linkage

Can someone tell me, and preferable show me a pic of where the adjustment screw is on a BBK TB? I am pretty sure I need to adjust it but I am not sure where it is.

There is a slotted screw on the TB to the left of where the IAC mounts, is this it? If so on mine it is screwed in all the way which does not sound right. I have the problem where the idle hangs up at 15-1600 RPM for awhile before it drops.

Thanks

Ron

glxieman@yahoo.com
 
I would expect it to be adjusted all the way in. You may need to turn down the throttle stop as well. You want it to where it hangs just slightly before settling. Usually about 1000rpm. It can be a very sensitive adjustment. Always turn the car off, let it sit for 15 seconds and restart after changing the throttle stop.
 
I think what you are talking about iadjusts the idle, not the IAC. There have been some pretty good writeups about the IAC adjustment process which includes elongating the holes and rotating the IAC until you get the right voltage reading.
 
I think what you are talking about iadjusts the idle, not the IAC. There have been some pretty good writeups about the IAC adjustment process which includes elongating the holes and rotating the IAC until you get the right voltage reading.

I think they do that rotating adjustment with the TPS, which should read about 0.95 volts closed.
 
I think what you are talking about iadjusts the idle, not the IAC. There have been some pretty good writeups about the IAC adjustment process which includes elongating the holes and rotating the IAC until you get the right voltage reading.

uuuuuuuuuuuh you mean TPS adjustments there.....? .97v
 
I believe that you are only supposed to use the second screw (the one near the IAC) if you can't get enough air bypass by using the throttle stop screw without making the TPS voltage exceed 1.2. IE, this second screw should let you make all the adjustments you need to without messing with the TPS too much.
 
I found an old thread about adjusting the idle. So I started with using the .010 feeler gauge likle the thread said to.

I then removed the IAC connector and tried to start it, but it would not start at all. I thought it should run 6-700 RPM with the IEC disconnected? When I reconnected the IEC it started up fine.

Took it for a short spin and the hanging idle was better. But...

Before this it ran fine except for the hanging idle. Now after it warns up even a little when I go to give it some gas it wants to buck and run crappy. Idle will sometimes drop to under 500 after idleing at a stop light

Is this all related or is there something else going on?
 
I think your suppose to set up the TB stop screw as indicated in that thread, then verify the TPS voltage.

Now unplug the IAC, get someone in the car to start it and you hold the idle and adjust the IAC screw open until the car can "barely" idle on its own, which should be around 500 rpm's or so. You'll need to goose the throttle after each adjustment and feather the throttle until she's running on her own.

Now plug the IAC back in and that should take care of that adjustment for you as tehnically that should land the IAC right in the middle of its control range so to speak. The TB stop screw should not be used to adjust idle RPM unless you have something very radical installed on your car.

If the car can't land at idle RPM when it comes down, thats telling me either the IAC is old and tired and can't recover fast enough, or you have way more air going in than the EEC likes for idle control, ie vacuum leaks, or a larger MAF are things that come to mind., and one of the symptom's is an idle that takes forever to come down.
 
That method sounds right. You may have better results by turning the car off before adjusting the screw, however. Then restart and recheck.

If your car can't idle without the IAC plugged in, even with you helping it until it settles down, then you almost certainly need more air bypassing the throttle.
 
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