ok, 93 F-150, 5.0 AOD

Drove from KY to FL and on the trip was running real rough before shutting off and when I started it back up again. Ran fine while moving, 15 mpg doing 75-80.
Took it to my Dads guy when I got to Fl and they smoke it and found the throttle itself leaking (not the gasket) and the EGR valve and EGR switch HOUSING gaskets leaking. All told, pretty good amount of vacuum leaks.
Replace TB with BBK, replaced EGR components, and IAC . TPS tested, re-smoked, no leaks. System electrical drained. Since then, truck runs fine with IAC unplugged. Even when running AC. Revs up when cold, idles down, idles fine, picks up idle when AC engages.
Plug in IAC, sounds like air suction picks up and it goes high, low, high low. Start up is VERY high, drops then goes to High, low again. rev it and it hangs high for a bit then drops, then starts the high low once again. Had an old IAC, replaced it, same thing. Double checked TPS, all in tolerance.
When I left FL, was told it would take 50 miles or so reset computer map. Made sense to me and they have a great reputation, so made the trip home.
When driving, runs fine except when stopping. Idles high, always wants to go because of it.
I've tested the TPS with volt meter, passes fine.

Any brain surgeons out there know what I to dot and T to cross for a solution?

 

Any KOEO fault codes?

 

My IAC has been unplugged off and on for over 30 years. It ran better and worked. Trying to tune these old systems in is sometimes more trouble than it's worth. I went the easy way after years of trying to get surge and high idle fixed.

No, to the purist, it's not right, but it works. I did every test and setting I could find. There was a great thread on here many years ago by a guy who specialized in these systems. I followed his directions to the tee. Nothing lasted more than a few days, if that.

I finally decided I would unplug the IAC, set the idle where I could live with it, then leave it alone.

The one thing I did do was put a push button on/off switch on the IAC so I could idle it up on a cold morning.

 

Hmmmm, I know it didn't when they finished it in FL, and I have no check engine light, but I did not hook up the reader.
Sounds like the next step I guess! lol

 

Check your fuel regulator is it getting correct vacuum and is it leaking? And do what the other fellers said they are some smart cookies lol. Wish you the best of luck!

 

How is the idle self adjusting for the AC and cold start with the IAC unplugged?

I’m thinking you still have a vacuum leak somewhere and the idle screw on the throttle body was adjusted to compensate for that leak and in the case of the AC cycling on and off, the engine is already running in a lean condition and just needs the extra fuel to increase the idle.

 

EFI - THROTTLE BODY/IAC - TSB 91-25-07 - IAC Bypass

https://www.garysgaragemahal.com/91-...ac-bypass.html

 

I had one of those on my bbk. Even putting a straight blocking plate, mine wouldn’t idle less than 1100rpm. You could shine a light through the throttle bores and see it behind. I even tried light sanding to get it to close, which helped, but I could never get the bores to seal enough. They work good if your cam doesn’t provide enough idle vacuum with speed density.

 

Ok folks...... update time for anyone reading this later.
I observed the butterflies not closing all the way. So looking into it further, 2 things- the throttle cable was not allowing the throttle to close all the way. Releasing the cable allowed a bit more movement to close. So I loosened the throttle cable mount and twisted it as far as I could and tightened it up, and bent the bracket slightly forward as well.
I also backed the idle screw all the way out and sanded the part of the throttle body where the throttle stop hits it. (the side the screw is in) It didn't take much, but ended up allowing it to close further. I figured even if I removed too much, I could just use the idle screw to fix it.
Reset the computer, reset the IAC and now I believe it is still a tad too high, there isn't the surging up and down as before. Also if she is revved up while in park, it seems to still take too long before she idles back down.
All in all, still don't think it's exact, but liveable! Maybe more driving will settle her down some more.

Thanks too all

 

By chance you didn’t inadvertently fill-up a time or 2 with E-15? Or possibly E-85?

 

Mr Lars- No sir, I don't believe I did, but what would that do?

 

Update for those interested.
After realizing that the butterflies weren't closing enough, I decided to play with it a little to see what I could do. So after removing the throttle body, I closed the throttle, and keeping tension on it to keep it closed, I loosened the torx screws holding the butterfly and gently tapped on the smaller gap side. That shifted the butterfly and I retightened the screws. LIGHTLY! I imagine if you adjusted too much it would cause them to stick and be harder to open.
Anyway, reassembled, checked TPS again, went thru the idle relearn process and lo and behold that puppy is finally running right!

Disclaimer- I'm just a dude playing a dude playing a mechanic....... try at your own risk!

 

The throttle should be close as much as possible without the blades touching the bores. If that happens, the bores wear and the blades catch causing the throttle pedal to be hard to press.

Good job fixing your problem.