Explanation of the Idle Air Control System ( IAC ) on an throttle body on a Crossfire C4 Corvette

[@gregmatherne7173]

Thanks Mr. Jay for the info, my next project is gonna throttle body and intake and I’ve been watching all your videos. Much appreciated! Have a great day sir!

[@84c4corvetteguy5]

Thank you, I appreciate you watching!

[@floridafishing]

Hello. I saw in the past several IAC who rotates and that’s the way they go out and in. I have question. At idle, the IAC should be totally closed? I’m having high RPM issue at idle after I rebuilt the TB. Ordered two new IAC but did not change them yet.

[@84c4corvetteguy5]

No they should not be completely closed. I believe on a scan tool mine read about step 8. If they were totally closed they could not function properly. If your idle is high and your IAC's are totally closed you probably have a vacuum leak somewhere or possibly you TPS or MAP sensor is sending the wrong signal to the computer Your TPS should read .55 volts +or- .05 volts at idle and you MAP sensor should be around 1.2 volts at idle. I hope this helps. Thanks for watching my videos!

[@floridafishing]

@@84c4corvetteguy5 replacing the IAC now. The originals are not totally closed but I can’t lower the RPMs. No vacuum leaks. TPS voltage good. Will check map sensor voltage but it is new OEM

[@floridafishing]

@@84c4corvetteguy5 worst with the new ones. Was 900 before, now 1200

[@84c4corvetteguy5]

@@floridafishing put your thumb over the IAC openings on both throttle body's or jam paper towels in the holes to clog them off, does the RPM now drop? if it does it 's bad IAC's or something to do with what is controlling them. If it doesn't you need to look for vacuum leak again. Hope this helps.

[@floridafishing]

@@84c4corvetteguy5 I tried that before. It does not. I read there is a vacuum hose going into the cabin for the AC vents. I can’t find that one. Could be that one. I put smoke on every single port and only is out via TB

[@vikingtrad3r]

Thnx again! My daughters i think my daughters car needs one or both new iacs. it takes forever to get the idle down to 800 rpm after startup. i hear the air rushing through the iac ports, with 1500 rpm, and either the ecm isnt commanding the iacs to close or they are taking thier sweet time. 2 questions: a. does anyone know how to test the iacs for proper function b. anyone purchased reliable new iac's confirmed to have worked and can provide a link pr brand/part number. thnx all

[@84c4corvetteguy5]

Put your thumb over the IAC opening on the throttle body see if the idle goes down, then do the same thing on the other throttle body. If only one of them make the idle go down that the one stuck open, if you have to plug both of them to get the idle to go down either both are bad or something else is telling them to stay open. Hope this helps!

[@84c4corvetteguy5]

you can use a scan tool to open and close them if they are working it will change the rpm. just remember you are dealing with 2 of them so I would block one of while testing the other. As far as reliable ones I really dont know it has been hit or miss I would probably go to Facebook Crossfire or another blog and ask. Sorry. PS: 1500RPM is good cold start up

[@vikingtrad3r]

@@84c4corvetteguy5 circling back. after watching your vid, i replaced the iacs with a set of spares i had. my spares were clean. what i pulled out was crusty and sooty. the car now controls its idle just fine. i now have only one runability item left to sort. the engine shakes alot while idling like it is missing. again, idle is now held fine at 700 or 800. when it gets down there, ithe engine has the shakes.u can see it shake. and u can feel it shake i recall your recent video working on a viewers car. u noticed the cone of fuel to be acone but not a pefectly smooth solid cone. i would say mine are not either. i have a spare set f injectors i will swap to see if the shake at least changes. btw, are you running the standard ts136 fan switch? it comes on at 100c. its perfect.

[@84c4corvetteguy5]

@@vikingtrad3r Yes, I look at it in Fahrenheit, on at 212 , but ya I run that standard part # switch. You will have to let me know what you find. Just remember the injectors are different part numbers. One is stamped 547 and the other is stamped 548. 547 goes to the drivers rear and 548 goes to the passenger front. They are stamped on the top. One flow slightly more do to the pressure difference between throttle body's. Please let me know how you make out.

[@vikingtrad3r]

Hey Jay, I have a request. Daughter and I are trying to sort out her idle. Ive just posted a video question regarding the behaviour of the iac pintle when a+b cavities on the aldl port are jumpered. Im not sure if i can link the video here but if you click my name you should see it. I would appreciate feedback.