How to clean K20 Idle Air Control Valve (IACV)

How to clean K20 Idle Air Control Valve (IACV)

I am making this post because… When i first started up my brothers K swap I was first excited that it was running well, but after a min of smooth idle it would begin to surge. Which as most Honda owners know its most likely a Throttle Position Sensor ( TPS ) issue or a IACV issue. So after checking my voltage and correctly setting the TPS the motor would still surge once it was warmed up. (bummer)I did some research online and came to the conclusion that the IACV needed to be cleaned. All the articles said just take it off the throttle body and spray some carb cleaner in it and bam it should be fixed. Seems easy enough, bought some carb cleaner took off the throttle body and took the IACV off , sprayed the carb cleaner some black stuff came out. Put the IACV back on the throttle body, put the throttle body back on the car, started it and same issue once it was warmed up, surge surge surge. I knew there was something I was missing so I took it back off and just figured it out for myself. Below are my results, step by step on how to completely clean your IACV so it works good as new. feast on the fruits of my labor.
So Step 1.

Is obviously take the throttle body off the intake manifold. you do this by taking a off  your intake, take off the throttle cable, remove the two small water lines that go to the IACV, disconnect the tps, disconnect the map sensor, disconnect the IACV plug, and there are 4 12mm bolts that hold the throttle body to the intake manifold. you should be left with this

As you can see the IACV is on the bottom of the throttle body.

Step 2.

Get a Phillips screw driver and remove the two Phillips screws hold the IACV to the throttle body, make sure you press firmly on the screw driver as to not strip the screws out. Stripping the screws out isn’t a life ender, but it would just be easier if you didn’t strip them out.

Step 3.
Pull the IACV off, it should come off with ease. Mind the rubber gasket and the two screws. I put the int he throttle body and set it aside so I don’t lose any of them.


Step 4.
You will now need to disassemble the IACV, this is the most tricky part. You notice that the IACV sensor has two “star” screws holding it together, they aren’t any Allen wrench sizes, and they aren’t torx bit sizes. Im sure somewhere someone knows what tool to you to take the screws out, but i just use a grinder with a cut off wheel and just make a small slit in the head of the bolt to make it a “flat head” screw now.




Step 5.
Take a fairly large flat head screw driver and apply direct pressure and turn counter clock wise to loosen the two screws. I realize that in the pics it is hard to see the slits i created in the screw heads.




Step 6.
Now the IACV should come apart and you will notice that there might be rust, or other gunk in both pieces, this is where you will spray the carb cleaner into both parts to clean it all out.




Step 7.
In the last picture from step 6 you see my left index finger is pointing to a small silver cylinder that has a small tab on it and a shaft the goes through a bearing. you must be able to freely spin this with your fingers this means that the IACV is going to be fully functioning. If yours is like mine and after spraying carb cleaner into it, it still doesn’t spin. then you are going to have to use some WD-40 or other lubricant to free the shaft and allow it to spin freely. this is very important, The way the IACV works is is by sensing how hot the engine is and it does this by reading the coolant temp as it goes through the IACV. once warm enough it will allow the shaft to spin around blocking a small hole that allows the car to have a steady low idle, much like a choke. if this shaft cant freely spin then it can’t properly block the small hole allowing air in, thus acting like a vacuum leak causing a surging idle.


Step 8.
 Now that your IACV is freely spinning with ease. ( note this might take some time, a lot of finger spinning, and WD-40 to continue to flush it out) if you don’t take the time to make sure it is freely spinning then when you put it all back together its probably still going to surge. now re assemble to IACV using the two screws you made slits in.


Step 9.
Re attach the IACV to the throttle body using the two Phillips screws and rubber gasket that you stashed in the throttle body for safe keeping. if you forget the rubber gasket then the coolant is going to leak into your throttle body.
Step 10. YOU’RE DONE!!!!!!! now just re install the throttle body and attach all sensors, hoses, throttle cable, and air intake. ( mine is missing a few sensor and im not going to be re installing it onto my motor, as the motor is currently not in the car and i need new gaskets) but this should help you get your car to stop surging.





8 thoughts on “How to clean K20 Idle Air Control Valve (IACV)

  1. Awesome Guide. Super helpful. Could you give me some tips on how the get the throttle body off once I have taken off all 4 bolts? I got to that step and just couldn’t get the throttle body off. I tried lifting it from underneath but it just wouldn’t move. Did you have to hammer it by any chance?

    1. If you’re talking about the throttle body off the manifold then yes you can gently tap it with a rubber mallet. Or use a soft piece of wood and tap that with a normal hammer. But be careful because there should be 2 bolts holding the throttle body on. And 2 nuts that are on two studs that stay threaded through the throttle body. It is however possible for the studs to have been removed and you having 4 bolts though. So if in fact you have 2 bolts and 2 nuts be more careful when tapping it with the hammer since the throttle body isn’t really going to move much. But if you in fact have 4 bolts that came out then you don’t have to be soo careful. But still don’t go crazy. I hope this helps and thanks for reading.

  2. Hi Billy,

    I got some issues too regarding the iacv. I swapped a Honda K20A2 into my Lotus elise.
    It started right away but the idlle was irregular.
    So I watched some youtube videos and dissasmbled the throttlebody and IACV. The shaft could not spin at all, it was stuck. So I cleaned it and reassambled it. The result was even worse…
    Question. After cleaning the valve cannot spin fully 360 degrees; it bumps on max opening. Does it have to spin 360 degrees so I have to clean it better? Do I have to position it (lip heading up or down or something like that) before refitting it?

    1. I would look into making sure you don’t have any vacuum leaks. If it was stuck and it couldn’t spin that was definitely a problem. It must spin freely to work accurately, i would double check to make sure it was reassembled correctly. what throttle body/intake manifold are you using. But honestly it’s going to be hard for me to diagnose thru the internet.

  3. Hi Billy, thanks for reply.
    I did not change any parts in the Honda K20a2 engine. So I’m using the original throttle body and mayfold. Since the IACV cannot spin freely I will heck it again. I will let you know if it is any better. Thanks

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