P0505 Idle control malfunction
 

Got a CEL this weekend on my '98 LS. I pulled a P0505 code out of it this morning, the description being "Idle Control Malfunction". The car was running fine and didn't seem to be idling low at the time that the light came on, but I have noticed the idle loping/surging after startup a few times on this car since I got it last week. I looked up the price for the IAC valve and nearly fell over. Please tell me that's the less likely cause. Do I just need to clean the throttle body and the valve?

Seeing how you just got the car you're gonna find out that parts for this thing are VERY expensive. You can try cleaning the throttle body. (can't hurt) But here's a link how to test and rebuild the IACV, if it needs it. It's alot better then spending $700 for a new IACV. http://www.planetsoarer.com/IAC/iac.htm

Thanks for the reply. That procedure doesn't look too bad. Actually I looked up prices for parts before I bought the car, and I found that for the most part stuff is reasonably priced, but when it comes to electrical components like solenoids and whatnot they're crazy expensive. That's something I'm used to with Japanese cars though. My other car is a '94 Miata and stuff for that is similarly expensive ($400 for a cam sensor for example). If it's just a bearing then I can handle that.

Test it first. You might not have to do anything to it, except clean it. Search the forum for whatever symptoms you're having and you'll find alot of useful info and other possible causes. It's possible it could be something other then your IAC, like maybe the TPS needs to be readjusted. Good luck on finding the problem.

cleaning the throttle body (spec. all idle air passages) may fix the issue.

Well I got a good look at everything today when I did an oil change. First I managed to break off the plastic nipple for the valve cover breather hose on the resonator box on the intake tubing. JB Weld to the rescue!!! Then I got a good look at the throttle body. That sucker WAS dirty. Cleaned it up good as new with some carb spray and a rag and I noticed an immediate difference when I started the car. It was idling at 1500 rpms, and stayed that way long enough for me to get worried, but gradually settled down as it remembered what it felt like to be new again. The idle is a lot more stable now, and seems to be at a normal 800rpms (before it was 500).

Interesting setup regarding the throttle body. At first I thought it was a regular throttle body due to the throttle cable, then I realized that it's actually drive-by-wire and that instead of having an electronic accelerator pedal everything's contained in the throttle body as one unit. What I found fascinating, which is something I haven't seen on any other car, is that if you step on the accelerator more than 3/4 of the way the throttle body is mechanically opened 1/4. That way if the DBW fails you're not stuck. Ingenious setup.

yep, '98 was the year the DBW was intro'd on the LS.

So my '99 threw this code today when I stopped to get gas. I plugged in my code reader and got the P0505 Idle Control Malfunction. My car has been running and idling fine as far as I can tell, I haven't noticed anything out of the ordinary with it. I went on ahead and cleared the code then drove it around my cul-de-sac, it didn't come back. I assume if I were to drive the car more the code would probably return. From my searching, it appears the best thing to do is clean the throttle body. I guess I'll give that a shot tomorrow. From what I've read, in order to clean the throttle body, the key has to be in the "acc" position so the throttle body will open. Is this correct? I want to make sure before I damage any expensive parts by doing something wrong. Here is the link I found for a GS400:

https://www.clublexus.com/forums/gs-...05-solved.html

Anyone? I'm going to try to tackle this later today.

It would be better if you just removed it from the car. Make sure to clean the passageway under the plate on top of the TB that's held down by the 2 screws.

I'll remove it as long as I don't have to drain the coolant. Thanks for the heads-up on cleaning under the plats, hopefully it'll take care of the problem.

I cleaned the throttle body on the car as suggested in the link above due to time constraints. Lots of black gunk in there and under the plate on top. After I felt I had everything good and clean, I pulled the ECU fuse for 30 minutes, then ran to the parts house to get a new air filter since the old one was dirty. While I had everything apart, I went on ahead and cut the extra air box I had for the air box mod. Once everything was back together I let it run for a few minutes before taking it for a drive. Once fully warmed up I did some spirited driving and man does this car still put a smile on my face! So far no codes, so hopefully I have it taken care of.

Glad to hear just a simple fix was needed.

I have a 2000 LS400 with the bouncing idle needle on start up with a small fluxuation then would go away. I ended up with VCS off and check engine light and the code P0505. I did a seafoam throttle body cleaning spray can kit and seafoam in the crank as well. The car has 199,500 miles it looked like the neighborhood was going up in smoke. I have had a few other weird codes so I may need to redo the ecu capacitors soon... Thanks for the thread hopefully this solves my P0505 problem.

LexusNAZ
Thank you for that post,please be sure to let us know what happens.