Idle Air Control Adjustment

OK, I have been having idling issues for months, and could not figure it out.
I had a mechanically inclined individual take a look at it.
He tweaked something near the IAC but I don't know exactly what.
Whatever he did brought the rpms back up but he told me
to replace the Throttle Position Sensor.
I did that and nothing happened.
Infact eventually the rpms fell to as low as it was before he began tweaking.
Nonetheless today I figured out it was the IAC itself all along.
I swapped that and now it idles but it is excessively too high.
I don't know what or where he adjusted.
where do I need to tweek to get the rpms back down to within specs.

Thanks

there is a stop screw on the throttle body next to where the throttle cable attaches. the standard drill for setting that screw is the following.

1) disconnect the IAC, if the truck stalls you need to turn the set screw in until is no longer stalls with the IAC unplugged. However in your cause it sounds like it is turned in too far.
2) with the IAC disconnected set the stop screw so that the RPMs are around or just under 500rpms
3) plug the IAC back in and the truck should settle to around 750rpms.


It's also a good time to check your TPS sensor voltage to make sure it is set to .95v

try that and let us know..

check the voltage first before you mess with the idle set stop screw... I have never had to adjust the idle screw on any of my engines, only the TPS and clean the IAC.

The IAC is not adjustable

The reason I recommended it, is it sound like his "mechanic" already monkeyed with it, and that is supposed to be the factory setup as best i can tell from the Ford Tech write ups..

you are right, if he adjusted the set screw to bring your idle up because the IAC was bad... and then you replaced the IAC and idle is way too high... the set screw needs to be adjusted. Good call!

Can you ask the mechanically inclined person what they did near your IAC and why they said replace the TPS?

High idle could also be a vacuum leak, so make sure you dont have one
The canister purge solenoid and many vacuum lines run in this area too, so wouldnt hurt to look around, make sure all wiring and hoses are good to go

Thanks for the info and insight it is appreciated.

I disconnected the IAC and the truck did stall.
I tweaked that set screw inwards until the truck wouldn't stall unplugged.
But the rpms have only dropped to about 900 from the 1000
it was when I first installed the new IAC. I may be doing it wrong.
I'll have to try it again tomorrow.

You need to reset the computer each time you adjust/clean or replace a sensor.

if you bolted on a new IAC valve and did not reset the computer that may be your issue.
Also when the computer is reset the idle may be high for a bit, until you drive it a few drive cycles the idle may be 800-1200 rpm....

What is this set screw you are talking about? the throttle body idle set screw?
I ask because I have added a part to my 96 truck that allows me to adjust the airflow bypassing the IAC valve because I am running a more aggressive camshaft in that engine

I tried unplugging the negative battery terminal to reset the computer.
I haven't seen much change.

This is the set screw I've tried adjusting.

http://www.geocities.com/jokerones212/pic4.jpg

Lots of good info in here.
Is that .95V with the throttle shut or WOT?

What exactly are we referring to when we say disconnect the IAC? Are we unplugging the sensor or unbolting the unit? A friend of mine unplugged the sensor while my truck was running and it immediately died. Please tell me he didn't screw anything up.

IAC = Idle Air Control module

it is the computer controlled valve that provides a bypass to the throttle body to control the idle rpm of the engine.



the .95v volts should be set with the throttle closed. you need to make sure you are testing the right wire. there are many writups on how to do this...