Autohaulers INC

I have an 01 GT with brand new motor and the idle is fine when sitting, even with the a/c on. The only time it dies is when im coming to a stop and im hard or moderate on the brakes? if i brake lightly it doesnt die...any ideas?? I read up on the IAC, TPS, and EGR....does my symptom point to any one of them??
it is only the long block that is new...the intake and everything else is the same as the last motor...

uberstang1

Does your speedometer work, this is also symptons of a bad VSS sensor.

Autohaulers INC

yep speedo works - what does VSS stand for

uberstang1

vehicle speed sensor

rsh0763

Mine was doing that.. I cleaned up the IAC and it resolved my issue. I want to say I cleaned the Bejesus out of it because it was BAD. Throttle Body Cleaner I think, but I had removed the stuff and made sure there wasn't a bit of anything left.

Bmitchell373

Check the throttle preset screw per Cliffys handy How to Page. And did you do the IAC mod?

Autohaulers INC

by the IAC mod did you mean clean it? can can I use brake cleaner or does it have to be throttle body cleaner...

Autohaulers INC

just cleaned the IAC and set the idle a tiny bit higher to see if this helps. I know you are not supposed to use the set screw to increase idle but I hope 100-200 extra rpm wont make a problem...its actually more for safety becasue when I coast to a stop and the motor goes, I lose brake pressure and pwr steering..

rsh0763

Well? Improvement? Or back to the drawing board?

cliffyk

It's not a question of "not supposed to use the set screw to increase idle" but rather that it will not change the idle speed for any but a short time. The PCM controls the idle speed to whatever is set in the tune by altering the duty cycle of the signal applied to the IAC. Adjusting the throttle stop screw only affect the idle until the PCM learns the new idle air trims--after that all adjusting it does is screw up (no pun intended) the IAC operating range. It is possible to use the stop screw to open (or close) the throttle plate to the point that that IAC can no longer control the idle at all--this or a failed IAC will cause the stalling problems you described.

The throttle stop screw needs to be adjusted as described here, otherwise the IAC will not be able to properly control the idle.

Back to your original problem it sounds as though you need a new IAC. Ford makes it clear in the shop manual that it cannot be cleaned, and those who have done so have generally found it to be temporary fix at best.