High Idle is usually cause by a vacuum leak at the IAC or the hose that goes to the air intake tubing. Had the high idle issue and it was the hose. I have a 75 mm BBK TB and have never had a problem with it.

 

Ok, finally picked up an IAC valve today...had to work late last couple days. I am almost done the job, will get it done tomorrow. Have been checking every hose in sight along the way. Hope this does it, was expensive, bosch $127 and motorcraft $214!!! Got the bosch, wish I had baby hands...

 

Changed the IAC and it was not the problem, still has the idle issue. Took the truck back apart tonight, and will put the stock throttle body on and see what happens. I looked at all the hoses coming from the IAC and intake, they are all brand new. I don"t have hose clamps on them, but the hoses are the proper size for a push-on fit, so I think I'm good there.

 

did you set the TPS after the throttle body swap????

 

Yes, I set the tps, the voltage was at 0.98, right where it was supposed to be.

 

Today I finally got the truck back together with the stock throttle body in place, and the idle went way back down, actually a little lower than it should have been (approx, 650rpm). So that means that the accufab throttle body was the problem (thanks FireGuy). I called them again, and they said that they would check everything for free if I send it back to them. I think I will try and send it out tomorrow, hopefully get it back quickly to see if I need to buy an LFP unit instead. Thanks for the help...I will keep you posted.

 

Good luck with that, I talked with the owner (Accufab) face to face and he tells me it is supposed to be that way. I just threw in the towel, sold the Afab at a small loss got the LFP and never been happier.

 

Ok, so I got the throttle body back from accufab, the said that they found that the throttle blade was not square in the housing and that is what caused the high idle problem. They send it back repolished and with a new gasket and some stickers (I was pretty impressed). It is installed on the truck and setup with the TPS voltage set at .982. The truck idles fine in drive, maybe even a little low in park. Everything seems to be ok...EXCEPT when I start the truck, it fires up right away like normal, but when the rpms come down, they come down too far and it almost stalls (this started when I put the stock throttle body back on to narrow down the problem to the t-body, but I just figured it was the stock t-body doing it because the truck was tuned for the accufab) I don't know what could be causing this....any ideas??? I might start a new thread late tonight of tomorrow for this problem just in case nobody is viewing. Thanks again everyone for all the help.

 

reset the ECM, and clean your IAC valve

 

IAC is clean, about resetting the ECM...I have disconnected the negative terminal of the battery for like 15 minutes and put it back on and that`s it. I am not sure of the proper procedure for resetting the ECM, I have read all kinds of outrageous stuff. Also will this erase the custom dyno tune on the truck and return it to stock? Sorry for the basic questions...

 

Sometimes cleaning the IAC won't do it. The replacements vary in quality, some have had problems after install. The best IAC is still the Ford one, but pricey.

I would have to do a search, but there is a procedure for setting the base idle on these trucks and Mustangs too. It was in another forum, I cannot recall right now. From what I remember, Start the vehicle, disconnect the IAC plug, set the TB so it just idles, not too high then plug the IAC back in.

Disconnecting the battery will not change the tune, it helps clear out old codes and allows the computer to re-learn and adjust to your setup.

BTW congrats on getting Afab to cough up on the TB, as I mentioned, they didn't help me at all.

 

Ok, so is just disconnecting the negative terminal on the battery resetting the ECM? I am still having the problem with it wanting to die just after startup, but it seems to happen only when the engine is cold. By the way, the idle is back up when I put the truck in park, not as high as before, it is around 950 to 1000 now, but it is still super annoying. Not too happy right now, I might end up being the new owner of a LFP SBTB...

 

With engine idling...spray some brake cleaner around the back side of the SC on the hoses coming off the fitting from the bottom of the turkey pan (see circled in red) and see if the engine rpm change any! This is usually the vacuum leak area with trucks with moderate to high mileage!

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