High idle problem

You can also use a 9volt battery and 2 small wires to touch the IAC male plug ends and see if the IAC valve closes. This will tell you if it's still functional and will allow you to clean it better with throttle body cleaner. Also replace your TB gasket is recommend, that was my problem.

 

thanks for the info and for the personal experience with the more in-depth cleaning process. I have some fipg layin around. did you just seal it back up with rtv/fipg?
And, as far as the O2s, exhaust gaskets and stuff, I'm not too worried about that at the moment, but I will take a look if none of this other stuff works.
The thing is, everything was fine before I dug into the VC/engine tune up job. No good deed goes unpunished, lol! I did the tuneup job bc the truck was new to me (with 230k) and i could smell burning oil. I knew the VC bolts were loose and all the plugs, tube seals, etc needed to be changed. The idle was fine before all this. I'm pretty positive that I buttoned everything up correctly, bc the engine is purring so nicely now but for the high idle in P/N. I really thinking it has to do with either the TB bore being too clean now (lol) or the IAC got extra gunked up during the original TB cleaning process I did.
I'll be sure to report back with any updates.

 

Yeah, I'm gonna work on this exact thing next - testing and likely recleaning the IAC. And here's another thing about the TB - from the PO, the truck has a TB spacer bt the TB and upper plenum, with its own associated gaskets. My plan was to remove the spacer and just go back to stock situation, also with a stock TB gasket..... but the 4 bolts are too long if I remove the spacer. So I just reinstalled it with the spacer for now until I can find 4 shorter bolts. (Hope all that makes sense).

 

The thing is, everything was fine before I dug into the VC/engine tune up job. No good deed goes unpunished, lol! I did the tuneup job bc the truck was new to me (with 230k) and i could smell burning oil. I knew the VC bolts were loose and all the plugs, tube seals, etc needed to be changed. The idle was fine before all this. I'm pretty positive that I buttoned everything up correctly, bc the engine is purring so nicely now but for the high idle in P/N. I really thinking it has to do with either the TB bore being too clean now (lol) or the IAC got extra gunked up during the original TB cleaning process I did.
I'll be sure to report back with any updates.[/QUOTE]


This is exactly what happened to me. my idle was much worse after cleaning but with the junkyard tb installed much better.

 

And Id bet if you pull the shaft which the butterfly valve is attached to while your idling, the idle drops down doesn’t it?

When you truck is warmed up go open the hood and pull toward to radiator on the piece that my fingers are on in the picture.

now shim the butterfly shaft with a split washer to ‘pull’ the butterfly valve inside the throttle body, toward the front end. This is what I did to temporarily fix my high idle until I have the time to send to max bore, I’ve now driven 20,000 mile or so with this repair and i still idle at 700 when my engine is 185

 

This is where I placed the shim to prevent the butterfly from slipping back into the groove that was worn into the TB

 

If it happened after I'd agree that it's most likely, tb, iac or you messed up. A bit more of personal experience, make sure you put the TB gasket on in the correct orientation, even if you remember putting it in correctly...

 

I take it you made a boo-boo on that gasket before lol.
On my truck, there is a TB spacer, and it has 2 gaskets on either of its mating surfaces between the TB and the plenum. I wanna remove the spacer and put a regular TB gasket, but I gotta find some bolts of original length, bc the bolts that are on now with the spacer will be too long for going back to the stock setup. So for now I left the spacer on, as is. You think I can just get some bolts at Home Depot, or do these bolts have to be specialty for auto use (ie dealer).
Where you at in Bama? I’m in HSV!

 

Yup, verified I had it right, bolted everything back together and had a massive vacuum leak. Not sure how I did it other than being an idiot lol.
Nothing wrong with any bolts, I doubt they're higher grade than 5.8, there's no real stresses on it.

I'm down in Auburn.

 

Roll tide!

 

What's that?

 

WDE!

 

Now that's proper.

War eagle!

 

Update: So, problem solved (mostly). I took your advice and ordered a cheapo IACV from Amazon. It actually had good reviews. Took off the throttle body and IAC, again. Sure enough, the throttle body bore had some light creeping through (pics below). ALSO though, I tested the old and the new iacvs with a jumper battery. The new iacv seemed to be opening and closing fine. The old junked up iacv that i had tried to clean up was not working. The little trap door would not open or close any further than the position it was in.
So, hooray, I installed the cheapo iacv, and my idle in P/N went right down to abut 1050 (instead of 1900). It's weird tho, I'm wondering what happened to that old iacv - it seemed to be working fine before i cleaned it and the throttle body. I guess i gunked it up too bad while cleaning the TB to save it. Or, maybe it wasnt working right before and the high idle issue was being prevented by the TB gunk. Maybe the TB was so gunked up that the gunk-ring was helping seal off that extra air from getting in?
Now, my idle is not quite right because of the bore wear, but it's a heck of a lot better with the new iacv. I can live with it and with the cheapo iacv until I decide to throw down the $400 on a new TB assembly.
Thanks for the help! I've learned more than I ever thought I would want to know about TBs and associated sensors.

 

Perfectly said! Great thought process man, you diagnosed this like a pro! Thank you for sharing