I did not plan on making a thread about cleaning the IACV on my 93 sc300 (132k miles), but the results fixed the idle issues I previously had so thought it was worth posting. You may want to consider doing this if you experience some of the symptoms that I have listed below.
Symptoms I Experienced
-After resetting the ECU, the idle would be low and it would take a few drives for the idle to reach normal again.
-At normal operating temperature: Random low idle.
-At normal operating temperature: Low idle then back to normal within seconds or with some throttle.
-At cold operating temperature: Turning the steering wheel at slow or at standstill (when power steering pump is engaged) causes idle to noticeably drop and seems to almost stall.
-At cold operating temperature: Random idle surge while driving within first 2 minutes. Feels like someone is pumping the brakes when you let go of the gas.
*For 1993 SC300 AT
Phillips screw w/ washer: 90079-11030
How to remove IACV on a SC300
I thought it would be a good idea to reset the ECU so I removed both battery terminals before working on the IACV. Removing the IACV is pretty straightforward as it is held down by 2 phillips screws. A problem you may run into is fitting a screwdriver into the bottom screw as the valve cover is in the way. Some kind of angled screwdriver or specific tool could do the trick. I did not have one so I loosened and moved the throttle body just enough for clearance. Also make sure to use a proper fitting screwdriver or bit to avoid stripping the phillips screws as they are on there pretty good. I almost stripped the bottom screw with multiple tools before realizing that I could remove the throttle body.
Once the IACV is removed, you can see if there is any sort of build up on the tip of the sensor. As for mine, it was gunked up with black soot and deposits probably accumulated from over the years. I used some maf cleaner I had laying around to clean off the build-up. Carb cleaner should work as well. I also took the sensor apart for a look inside, but seemed clean so I did not mess with it. Wish I took before and after pics, but again I was not planning on posting.
Before reinstalling, I also removed the intake pipe by the throttle body and sprayed some maf cleaner into the IACV chamber which is the bottom hole as you look into the throttle body. Make sure to put some kind of rag or paper towel to catch all the liquid that flows out where the IACV was installed.
To reinstall just reverse the steps. Reconnect your battery terminals, double check installation, and fire her up. Hopefully this will cure some of your idle woes.
All the symptoms that I listed above are now non-existent in the past week and a half of driving the car. There were no low idle issues after resetting the ECU. There have been no random and strange low idle issues. The cold start idle is also lower at about 1.5k rpms instead of the 1.9-2k rpms it was before. The idle is now nice and smooth. I keep a mpg log so I'll update this to see if it made any kind of difference on the next fill up. In my opinion, this is totally worth the time as the issues often times puzzled and frustrated me.
Symptoms have not come back at all. The idle is still smooth!
Also go here for some pics and info of the IACV: http://www.planetsoarer.com/IAC/iac.htm
Tip of the IACV that was cleaned (courtesty of http://www.planetsoarer.com/IAC/iac.htm