I just bought an 03 GS430 with the same condition,we've had others come thru the shop and everything we tried has failed. I cleaned the throttle body and puled the efi fuse to reset the ecm memory and it worked so far but its only been a couple of days.

 

Hehe, now i wish i wouldn't have said that. Now i experience a very random low idle, after heavy footed driving then coming off the freeway and sitting at a light, i notice the idle was below 500rpm, and my tach is about 150rpm off what the Techstream says my rpm is. I am very interested in figuring this one out.

I noticed the low idle as i pulled off the freeway on my way to work, so i was just going to plug in the scan tool, and read the info, then shut it off and then start it back up. BUT i forgot, and i shut it off, and then i started it right back up, and it now idles around 1000, so i let it idle for 5 mins or so, and never dropped below 800.

 

When I brought my car in for my 60k service I made a big fuss about the low idle issue. My dealership said that they would arrange a meeting with me and a Lexus Engineer at the dealership. The engineer went for a ride with me and noticed the idle vibration. He said that the reason for the low idle deals with emmision requirements. I dont know if that is a bogus reason but that is what he said he tells everyone.

 

Hrmm... Sound fishy, but that doesn't mean that he is lying.. But then agian, would you trust him if he said he had no idea?

 

Ok guys I just wanted to update you guys and tell you I was having a low idle problem. I figured it might need a tuneup so I changed out my plugs and air filter and it seemed to do the trick. Havn't had the low idle problem in about a month now.

 

Where did I say that he has no idea?

 

Sorry, i did not say that you did say that. I was just saying, he seemed to think it was emissions related, and i don't understand how that could be the case. I guess i am just confused to why he would say it is programmed into the emission control. Since our cars has an electronic throttle which controls idle, i think it has to do something with either programing or the blade itself, but then agian my guess is as good as his. All i was saying is that if he were to say "I have no idea..." Would you believe him regardless of what he says, or would you think otherwise, that is all i'm saying.

 

I would check your coolant temp sensor readings, also check the voltage difference between you acclerator position sensor and your throttle position sensor. This is very important to maintaining a steady idle

 

Low idle is good as long as you don't stall. You burn less gas cause your motor isn't turning over as much. Saves money in my book over the long run.

 

not when the engine is shaking and vibrating the whole car.

 

Mine doesn't vibrate , just a light whallop noise as the engine turns over at low rpm. My car used to vibrate till I got new engine mounts put in , but not any more.

 

That is not necessarily true, it depends on what your short term fuel trim is. If the vehicle is idling rough, i'd imagine that the fuel delivery is the same, being within 200-300 rpms. I can't imagine that, that much fewer rpms will not make as much of a different than that of a higher rate of speed. At idle your vehicle is running very lean already, and the vehicle is going to constantly adjust fuel trim to maintian the programmed data in the ecu.

 

Just to give an update on my situation....it seems that mine has been resolved for now.

I had super low idle issues forever. I had noticed that my voltage would always be super low as well, which I attributed to the low idle not turning the alternator at the speed it should. I constantly had to keep a charger on my battery to keep it fully charged. Even with all my mods, I've never believed that the car SHOULD low idle. I'd always thought that it was an ECU glitch since cars in our gen. seem to have it regardless of mod levels.

Anyway, about a week or two ago I got the dreaded CEL. I pulled the codes and it had all kinds of new codes. They all had to do with the throttle body. I changed out the TPS, and it didn't fix the issue for long since the codes came back. I did some reading and found out that when the ECU sees any of these codes, it shuts down the valve motor on the TB and then the car only idles via that throttle cable. So in essence, you're left driving with two feet to keep the car from stalling. For those that don't know, a NEW TB is $1000+ at the dealer. Luckily I have some great friends and one of them pulled some favors and got me a used one at a great price. I put it on and VOILA!!!!!!! My car idles perfectly now. No longer do I have to have the A/C on to keep from stalling. No longer is my voltage constantly at 12v at idle, since I now idle where it's supposed to.

Anyway, since the TB has 3 different electronic parts that have to work together to keep the car at idle correctly. I suspect that one malfunction doesn't trigger the meltdown, but 2 or more bring on Armaggedon.

BTW, my VSC lights (both on and off) lit up every time there was a bad TB code. Don't know the correlation of the two, but the car went funky as soon as both those lights would tilt.

Well, I thought I'd share.

 

I have a 98' ls400. Could any expert out there load the pic of IACV and TPS. I could not located. Thank you

 

same problem, low idle, most noticeable when hot, some times drop out of now where then come back up. Idle mostly around 550 500 drops to 450s. I have a obd scanner with live data and ive been checking it before i replace my tps. Sometime i see it will switch back and forth to 13.1 and 12.7. Car still off wide open throttle only make it to 81.0 and sometimes continuously switches down and up .4%. Car running the % is lower at 11.7%. I could be off on the exact % as i checked it last week and i am away from home. I do remember the .4% change and wide open position. Is 81% wide open normal????????? Shouldnt it be higher? Anyone else have a scanner to check there tps with? Im also doing my mounts soon as they are bad.

i also had the same problem as jmercbr900 which had to do with the throttle control motor. I disassembled mines and ran 12volts to the motor and in gauged the clutch. Reassembled and the code/problem never came back. Guess i got luckey. Im hoping its the tps since its a cheaper part to replace and that .4% change ive been noticing. It is also some what adjustable so im praying this will fix it


When i get home i will post my tps % before and after i change it. i would encourage everyone else to post there live data along with anyone that doesnt have an idle issue