分享：有关IACV清洗的心得(欢迎拍砖）

(It’s easier for me to type English. See my yesterday's posting for some background info.)

I think IACV (idle air control valve) stuck/sticky issue could be common. Since last night I took advice (thanks to “gonowhere1” for his suggestion) and actually did it myself and successfully turned a possibly $200~300 job into a few dollar work(plier, Philip screw driver/wrench and a can of sensor cleaner). I’d like to share my piece of mind to people who have not done it but might be interested and still intimidated by the acronym. (BTW, after last night’s 2hr IACV cleaning, I made a 150+ mile long trip today and so far it idles so well.)

First, it’s not as difficult as it may sound. Pretty much just taking down the air intake hoses to open up working area, unplugging the electrical connection to the IACV , taking down two screws that fixing the electrical coil and do a bit cleaning and that’s it. Once I did it the first time myself, next time it should take me less than half hour to do it. But there are few things need to be cautious for the first time.

Mechanism and failure symptom: This IACV is a motorized valve to control the air intake for idle speed. When idling, the main throttle valve(s) (large diameter) are off(unless you press gas pedal). So if the IACV is stuck (some people say due to carbon build up, but I thought it’s more likely due to particle from air after the air filter), the valve, supposedly controlled by computer based on RPM setting, can no longer function properly. It may be stuck in a position that the little air is insufficient to keep engine running. If I keep pressing the gas pedal, what it does is to open the main throttle valve(s) to feed in air. This explains why I could keep the engine started and running only if I keep pressing the gas pedal. It’s the air instead of fuel that’s making the difference when pressing the gas. Some people say rough idle may also be due to IACV issue. Once you understand this, it may help to differentiate other problems like fuel filter related, etc. You can diagnose yourself based on this mechanism understanding.

Steps for simple cleaning:
1. I suggest you registering as a Lexus club owner (just make up a Lexus model if you don’t have one) so you can access this step by step procedure (with pictures): http://us.lexusownersclub.com/forums/index.php?showtopic=30723&hl=iacv

2. This linked procedure is for Lexus, but the pictures show exactly the same parts as my 03’ Avalon. I think all vehicles are in principle similar in term of the configuration, but may differ in form and shape once it comes to the parts.

3. How to identify IACV? Go on line and find your IACV part and see how it looks like. As for the location, first find the air filter. That’s a big box with a large diameter hard plastic hose (like vacuuming hose, it’s called in-take hose) connecting to it. This plastic hose should be connected to another manifold air-intake metal piece which connects to the engine. This is the throttle valve control part (you may see spring-loaded wire connection which controls throttle valve that can open/shut to control air flow when pressing gas pedal). The IACV piece is right next to the main throttle (throttle body).

4. How to take things apart? First, remove the in-take hoses by disconnecting from both air filter box and engine throttle valve body. This will expose the IACV piece. (You may need to disconnect few other small hoses that connect to the in-take hoses so you can totally remove it out of the way.). Then unplug the electrical wire connection. This will expose IACV piece. After remove the screws that fix the plastic piece on the IACV, this will pop out and exposing a pencil like metal piece. Turn this metal piece, it should rotate smoothly within limited range. If not, you may have just found your car problem since it means that something make it stuck. Turning the small shaft back & forth until the turning becomes smooth. This is the motor axle controlling the idle valve. I used sensor cleaning spray to clean the area (be careful with the rubber seal and metal washer which may come out).

5. I pretty much stopped there and didn’t go further removing parts. The Lexus club procedure link suggests go further by taking down the whole IACV, which is attached (underneath) to the throttle body. I found it too difficult to move the tools to take out screws without damaging the screw themselves. Now I just put everything back together in reverse order. Once engine is started, the initial idle speed appears to be higher than normal. But after few minutes idle and driving it adjusts itself to normal.

6. Two things need to be very careful: first, the screws that you try to remove from IACV are very soft. Make sure use a Philip type wrench that can fit it snugly. Otherwise, it may slip and make them very difficult to remove. The 2nd thing is that after removing the coil (plastic piece) from IACV, the metal shaft (pencil like) is exposed and there is a rubber seal and a metal washer in there. Make sure don’t drop them. Otherwise you may find it very hard to locate them in the engine area. I was lucky that I notice them when they partially fell out of place.

Have fun.