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IACV delete? Who's done it?

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    IACV delete? Who's done it?

    I read some posts where the IACV has been blocked off. What are the down sides to this? Bad MPG? Any bad effects? Should the hoses be rerouted for this? i wanted to do this to my swap cause only after i unplug my IACV, then my car idles ok. No surge. i just have to adjust the idle a bit.

    #2
    your fast idle valve is probably bad if you unplug the iac and it runs fine. ive also seen the air booster valve upside down cause this. also check for vac leaks. you can delete it but it runs like hell when it gets cold out.

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      #3
      Probably some of my posts? The down side is that the idle speed won't be able to automatically adjust when there is an auxilliary load on the engine (e.g. AC, lights etc). Load from the AC compressor or from the alternator (when it's working hard) cause additional 'drag' on the engine, causing the idle speed to drop, which can then cause the engine to vibrate unpleasantly. The computer detects a low idle and then causes the IACV to open until the idle rpm is at spec, but with a blanked off IACV no air can flow through it so no matter what the computer tells it do it makes zero difference.

      My experience is that (with blanked off IACV) setting the idle speed at the throttle body idle screw so that the idle is on the upper side of the spec idle rpm range (i.e. about 800rpm) means that while the idle still drops with auxilliary loads, it doesn't drop into the range that causes unpleasant vibration. This is with my car, I can't guarantee the result on yours.

      The IACV has no affect on engine operation above idle speed, or when the engine isn't operating on the 'overun' (i.e. overun being when the throttle is closed but the engine is still rotating above idle speed), so there should be no difference in fuel economy with or without the IACV operating. I certainly didn't notice any change in economy after blanking of my IACV, and I can't see how it possibly could have any affect.

      The only change you need to make after blanking off the IACV is to adjust idle where it needs to be with the throttle body idle screw (but don't confuse the idle speed screw for the throttle stop adjuster, which is next to the cable pulley, don't touch that). Leave the hoses etc alone, unless you really want to stop coolant from reaching the IACV so it doesn't add heat to incoming air (in reality an unimportant issue since the amount of heat involved is minimal).

      The upside of blanking off the IACV is improved drivability associated with rpm dropping more immediately when shifting to a higher gear, and more consistent rev matching when shifting down because the engines response to 'blipping' the throttle is more consistent.
      Regards from Oz,
      John.

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        #4
        it makes no sense to me to remove it. its there for a reason - to maintain quality idle speed esp when cold and under loads. the gains are not worth it but to each their own.
        Last edited by king_cobra; 09-03-2008, 07:22 AM.
        '93 EX-R 5spd

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          #5
          Originally posted by king_cobra View Post
          it makes no sense to me to remove it. its there for a reason - to maintain quality idle speed esp when cold and under loads. the gains are not worth it but to each their own.
          The point of disabling the IACV is so that the rpm are not held momentarily high (or even rise slightly, as occurs in some cases), and / or prevented from falling promptly, during gear shifts. IACV action also causes rev matching (when downshifting) to be more diffficult.

          This behaviour affecting rpm (at rpm higher than idle) when the engine is on the overrun (as when shifting gear) is a function of the engine management, the IACV only being the 'tool' that is used to achieve it. This function of the IACV is a function dictated by the need for meeting pollution control requirements (reduces oxides of N I believe), not for any other reason, and is seperate from the IACV function of maintaining spec idle speed.

          This is only an issue for manual trans cars, it's of no consequence for autos. Disabling the IACV improves gear shifting quite a bit in my experience. Note that I said "disabling", and not 'removing'. Removing (or electrically disconnecting) the IACV will be detected by the computer, which then causes a CEL, and also causes the computer to do something that causes on / off throttle behaviour to become harsh (associated in some way with fuel injector cut out on the overun).
          Last edited by johnl; 09-03-2008, 06:12 PM.
          Regards from Oz,
          John.

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            #6
            Originally posted by king_cobra View Post
            it makes no sense to me to remove it. its there for a reason - to maintain quality idle speed esp when cold and under loads. the gains are not worth it but to each their own.
            Like Johnl says it is not removing it but rather blocking it. I did this today and my car idles way better than before. No more surging from 1000 to 1500 rpm. i did have to increase my idle screw. I've tried lots of things before like switching IACV ( 3 times), switching and adjusting FITV, vaccuum lines new, new gaskets, and TPS adjust. This is my only solution right now for my crazy idle. Glad i came across Johnl's posts. By the way, how will the car act in the winter time? By the way, i have a H22.

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              #7
              I've tested my car with an IACV delete (was planning on doing it on my H23/A6 intake manifold swap).

              55F morning, started the car up, holy hell it ran like crap and it really wasn't all that cold. I'll never do that again.
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                #8
                ^Weird, I've had mine blocked off for awhile now, def. used to it, also makes the flywheel "seem" lighter just b/c the IACV will delay the RPM drop. I'm in the process of doing something new and more involved w/ it.

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                  #9
                  Originally posted by Granite CB7 View Post
                  I'm in the process of doing something new and more involved w/ it.
                  You tease, do tell...
                  Regards from Oz,
                  John.

                  Comment


                    #10
                    Originally posted by frootloops View Post
                    I've tested my car with an IACV delete (was planning on doing it on my H23/A6 intake manifold swap).

                    55F morning, started the car up, holy hell it ran like crap and it really wasn't all that cold. I'll never do that again.
                    I would suggest that this is probably being caused by the FITV not functioning correctly, rather than because the IACV was "deleted".

                    The FITV should be able to increase cold idle speed adequately on it's own without assistance from the IACV. If the cold idle is too low (i.e. FITV not working properly) then the IACV should step in to some degree, but my understanding is that this isn't really it's job.

                    Do you really mean "deleted", or blanked off? Deleting or disconnecting the IACV from the wiring harness isn't a good idea (result will be the same in both cases, not pleasant).
                    Regards from Oz,
                    John.

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                      #11
                      I am just curious how you guys do block off the IACV? KMS and anyone makes an EGR one, is this a similar situation where others make this block plate?

                      Also is it beneficial to just bypass this (plug the ends of the IACV) and run straight to the FITV? i read something about heat, so I am just curious now.

                      Hola, tengo tres patas. Me llamo tripod.

                      Originally posted by d112crzy
                      So you're throwing a bitch fit because some other girl at school has the same nail polish and skirt as you do?

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                        #12
                        Soda can block off plate.

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                          #13
                          Originally posted by d112crzy View Post
                          Soda can block off plate.
                          i had a feeling i was gonna get that response lol. thats what c-los wanted me to do for the egr at the time lol. i said nah, ill spend the 15 and get a real one. what about since it will have vac? do i just use some rtv or something? i mean the iacv is gasketed so it doesnt leak.

                          Hola, tengo tres patas. Me llamo tripod.

                          Originally posted by d112crzy
                          So you're throwing a bitch fit because some other girl at school has the same nail polish and skirt as you do?

                          Comment


                            #14
                            A block off plate is a block off plate.

                            Making it look pretty is another thing.

                            I like my pepsi block off plate.

                            CrzyTuning now offering port services

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                              #15
                              Originally posted by d112crzy View Post
                              Soda can block off plate.
                              Perfectly adequate, but I can feel smugly superior because mine is made from genuine engineering grade brass shim.

                              Use a smear of non hardening gasket goo on both sides of the blanking plate.

                              You can bypass the coolant hoses if you really want to, but it's no big deal. The amount of heat that can pass into the inducted air from either the IACV or FITV is miniscule, I doubt you'd be able to even measure any performance gain on a dyno.
                              Last edited by johnl; 09-12-2008, 11:32 AM.
                              Regards from Oz,
                              John.

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