解决车不能保持怠速的问题 - 清洗 IACV（Idle Air Control Valve）

车能启动、但不给油的话就熄火，家里的 old workhorse Lexus RX 300 就出过这问题。解决的办法是清洗 IACV（Idle Air Control Valve），网络上有详细的说明（在下面）。

过程中的难点只有一个，就是下图中绿色箭头所指的那两个螺丝被原厂家拧的太紧了，而且材质比较软，用平常的螺丝刀拧不下来，如果用力过大就很容易把十字螺丝口拧坏了。

需要到 Harbor Freight Tools 买一个特殊工具  impact screwdriver:

里面长这样：

用锤子敲手柄的顶端就可以借力把因为生锈而很难拧动的螺丝拧松。注意要把接在这个工具尾部的螺丝头面对自己时逆时针拧到不能动位置才是 unscrew setting. 

我事先在那两个难点螺丝上喷了几次 WD40，又用锤子接上螺丝刀敲击使之松动，最后用 impact screwdriver 挺容易地拧下了靠里面的那颗螺丝，外面的花了更多的时间和力气，用  impact screwdriver 先拧紧再拧松几次，最后终于成功了。这个螺丝帽的材质实在是太软了，下图里右边的螺丝口已经有点花了，但幸好没有完全破坏它。

注意上图里那个黑色的圆环又小又细，是套在大的器件后面的，拿下来的时候要非常小心，不然就很容易脱落弄丢了。

然后用 carburator & choke cleaner 彻底清洗下图里的两个进气口（需要打开里面的 butterfly valve 清洗，进气口上面靠前的地方有打开 butterfly valve 的弹簧开关）、靠内的那个进气口里面的小孔、和下边那个小的圆柱形 valve, 要让这个 valve 很轻松地刚好来回转动90度，如果转动能超过90度，那么这个器件就已经损坏了，需要买个新的换上。没清洗之前如果它被积碳阻止没法自由转动，车就会因为给气不足导致怠速太低甚至熄火。

清洗干净、用干净纸巾和 Q-tips 擦干、空气晾干后，再把所有的东西照原样装回去。第一次启动车的时候引擎会稍微迟疑几秒钟启动不了，需要多给点油帮它转起来，之后的几次熄火再启动就一切正常了，看一下怠速也在正常的范围内。

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The Idle Air Control Valve, or IACV which I will be referring to it as, is very commonly clogged with carbon/dirt deposits and overtime becomes less efficient and unable to do it's job as controlling air flow to the engine during idle (butterfly valves are closed so it redirects air). With that said, the common symptoms are rough turnover from cranking to idle, having to throttle lightly to stablize the engine, and even not being able to idle the car for periods of time.

I'll try my best to make sense and walk everyone through how to simply clean the IACV and if anyone as questions feel free to ask, I'll answer to the best of my ability.

First thing's first, gather the proper arsenal for any battle, what isn't pictured here is safety glasses which everyone should wear, I'm wearing mine as I took this picture.



Pop the hood, and remove the airbox lid. The red arrows are pointing to two metal clamps which pop off, and the green arrows refer to two plastic pieces which you slide to the right (direction of the arrows) to remove the lid.



Next, are three 10mm screws which are also hexes. Since they are I chose to go the socket wrench with 10mm socket to loosen these. They do not have to come off just loose enough for you to remove the hoses from the throttle body. The first screw I'm shown removing in the picture removes the airbox lid from the hose, the second and third screws in the picture remove this hose from the throttle body, when everything is loose just pull and move out of the way of the throttle body.



Now here is a picture of your exposed throttle body. The 1MZ-FE in our RX300's have two, the right (Closer to firewall) of which contains the IACV. It's the black motor outlined by my green arrow. The red arrow is where air is redirected during idle times and where most of the deposits build up and mess up the idling.



Unplug the wire leading to the motor, it's just a clip-off. This part was fairly tough if you're impatient, you need to remove the two bronze screws but they are extremely soft and the Lexus/Toyota techs have overtorqued it. You may work at it with your snub screwdriver but if ***** hits the fan then get yourself a small vise-grip, clamp on the head and twist. Should break the seal here. Be CAREFUL as these screws are soft, be patient. 



Once removed this is what shows, the bottom is a lever that rotates to open/close the IACV. Try rotating it, if it is sticky then this is a sign of deposits clogging it up, not allowing it to open/close freely causes the idling problem.

Here you want to take your can of throttle body cleaner, spray into the valve opening and use your other free hand (not shown as I was taking the picture) to rotate the bottom part. Once you can rotate the bottom lever without any resistance your IACV should be fine. Take some extra time to continue to clean the butterfly plates and use a few Q-TIPS to clean the area leading into the IACV.



As stated before, be careful when putting the screws back on. Re-clip the wire to the motor. Take some time to carefully put the intake hoses back onto the throttle body, tighten the screws and put the airbox lid back in place.

After you double-check everything make sure that there is no equipment/tools left lying in the engine bay and fire her up. You may need to give a little throttle on your first start-up and she may choke on it a little but then it should smoothen out. 

Congratulations and go wash your hands, unless you wore gloves.