idle air control valve problems on a 91 5.0
 

I have a 91 5.0 mustang with a 5 speed. The motor is pretty much
stock execpt for roller rockers, headers, pulleys, the mass air
meter, 65mm throttle body, and a cold air intake. The vehicle was running fine with this combination. In fact it was running quite well until I put a Trick Flow street intake on it about a month ago. What happens is that the vehicle idles good and runs very well, but when I start to come to a stop and lets say I'm running 2k rpm and I push the clutch in and take my foot off of the accelator it sometimes wants to shut off. The vehicle cranks up fine and runs normal, but its annoying to have it shutting off while I'm coming to a stop. One mechanic told me it was either a vacume leak or the IAC valve. I checked for vacume leaks and could not find any. I replaced the IAC valve with one from Advance Auto Parts, and it doesen't shut off as much as the stock unit, but every once in a while it will. Any help will be appreciated. I have to fix this problem. Thank You.

Re: idle air control valve problems on a 91 5.0
 

You've changed the airflow into and out of the engine. What is happening is that the idle dashpot isn't sufficient enough to keep the engine from stalling on de-clutch. A good tuner would be able to adjust the idle preposition, dashpot and isc neutral air to restore the driving quality. Word of warning, if you attempt to add idle air by adjusting the idle stop screw on the throttle body, you'll most likely end up with a flare on the shifts and a surging idle. A custom tune is really the way to solve the driveability issue.

Re: idle air control valve problems on a 91 5.0
 

Thanks Brett! You inadvertantly got that question answered for me as well. I don't want to take over thread, but what is a dashpot/ idle preposition/ isc neutral air? Does someone have a link showing how to do this one? I got major surging after fixing my vacuum leaks and adding a 1" spacer... Sorry Brett- I fugured you might ask anyway. :D

Re: idle air control valve problems on a 91 5.0
 

These are all parameters or tables found in the PCM. They have to be accessed & changed through a custom program (chip). We use the SCT Advantage (Superchips Custom Tuning) at our shop but a shop using Autologic, Diablosport/Chipmaster, or other custom tuning software can make the necessary tuning changes for you.

Re: idle air control valve problems on a 91 5.0
 

Jeff, thanks for the info. I don't have my Stang anymore, but I fought that problem for years with it. All the IAC changes, resetting computer, changes to throttle screw position, etc. never seemed to totally eliminate my problems. This is the first I've heard of the parameteres you mention. Good info to know for future reference. Thanks! ( I am already planning out my next Stang purchase for this spring...the Conturd has got to go :D)