解決車不能保持怠速的問題 - 清洗 IACV（Idle Air Control Valve）

車能啟動、但不給油的話就熄火，家裏的 old workhorse Lexus RX 300 就出過這問題。解決的辦法是清洗 IACV（Idle Air Control Valve），網絡上有詳細的說明（在下麵）。

 

過程中的難點隻有一個，就是下圖中綠色箭頭所指的那兩個螺絲被原廠家擰的太緊了，而且材質比較軟，用平常的螺絲刀擰不下來，如果用力過大就很容易把十字螺絲口擰壞了。

 

需要到 Harbor Freight Tools 買一個特殊工具  impact screwdriver:

 

裏麵長這樣：

 

用錘子敲手柄的頂端就可以借力把因為生鏽而很難擰動的螺絲擰鬆。注意要把接在這個工具尾部的螺絲頭麵對自己時逆時針擰到不能動位置才是 unscrew setting. 

 

我事先在那兩個難點螺絲上噴了幾次 WD40，又用錘子接上螺絲刀敲擊使之鬆動，最後用 impact screwdriver 挺容易地擰下了靠裏麵的那顆螺絲，外麵的花了更多的時間和力氣，用  impact screwdriver 先擰緊再擰鬆幾次，最後終於成功了。這個螺絲帽的材質實在是太軟了，下圖裏右邊的螺絲口已經有點花了，但幸好沒有完全破壞它。

 

 

注意上圖裏那個黑色的圓環又小又細，是套在大的器件後麵的，拿下來的時候要非常小心，不然就很容易脫落弄丟了。

 

然後用 carburator & choke cleaner 徹底清洗下圖裏的兩個進氣口（需要打開裏麵的 butterfly valve 清洗，進氣口上麵靠前的地方有打開 butterfly valve 的彈簧開關）、靠內的那個進氣口裏麵的小孔、和下邊那個小的圓柱形 valve, 要讓這個 valve 很輕鬆地剛好來回轉動90度，如果轉動能超過90度，那麽這個器件就已經損壞了，需要買個新的換上。沒清洗之前如果它被積碳阻止沒法自由轉動，車就會因為給氣不足導致怠速太低甚至熄火。

 

清洗幹淨、用幹淨紙巾和 Q-tips 擦幹、空氣晾幹後，再把所有的東西照原樣裝回去。第一次啟動車的時候引擎會稍微遲疑幾秒鍾啟動不了，需要多給點油幫它轉起來，之後的幾次熄火再啟動就一切正常了，看一下怠速也在正常的範圍內。

 

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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.