DeLexus

1999 Ls Low idle

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Hello everyone, this is my first post so please excuse me. I have a 1999 LS 400 with just over 90k miles. I recently noticed I have a low idle of 400 when in drive, and only drive (D,4,3,2,L). In reverse it is 650. In park or neutral 850. 

If I turn the headlights on the idle is becomes 600 in drive. The other idles remain the same as before. Also, if A/C is engaged the drive idle is 600.

I cleaned the MAF sensor and did a spray cleaning of the throttle body (removed air intake hose and sprayed butterfly). 

I have no check engine light and the car runs good other than the low idle. I also always use premium fuel. 

I am just puzzled that the low idle is only in Drive, and not Reverse.

If anyone has any insight or ideas I would greatly appreciate some input. I do apologize for the long post, but wanted to explain as best as I could.

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Hi David...welcome to the Forum

I'm not entirely sure if you can raise the base idle speed electronically through the OBD port but if not, then I suggest looking for vacuum leaks and alternatively running some cleaner through the engine to clear out the carbon build-up and giving the engine a good blast...tends to cure it.

Let us know how you progress with this problem

Cheers  Trevor

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Thank you Trevor,

I actually disconnected the battery yesterday to change the terminal connector, and now I reconnected the battery the idle is very bad! Now upon startup, warm, it drops down to 200 rpm in Park! I made an appointment with the dealer to see if they can figure out with what's going on.

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Sometimes, the engine management system needs to relearn the settings so after disconnecting/reconnecting if you take it for a drive using half open/closed throttle settings and putting the air con on along with lights to load the system so the idle speed can be relearnt.

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My car idles at around 400 in drive. As these cars age most of them idles around 400-500 in drive. I would not worry about it. Once when my car was idling around 200 It shutdown several times in heavy traffic. First thing I did was clean the MAF which improved the idle immensely.

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Thank you for taking the time to read and reply to my post. I had a little update, I brought the car to the dealer to have a fuel system and throttle body cleaning and then reset (disconnected battery) to give the car a whole new start with a clean beginning. I am driving it to let it relearn the idle. As of now I think it's still learning but hopefully in the next few days it should be ok. I will keep you posted. 

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Hello everyone, here is an update. My car still has the problem where the idle is all out of order. After the disconnection of the battery really messed everything up. It starts, idle immediately drops to 600-200rpm then the engine kicks back up to 800-950rpm. One dealer told me to drive it and put miles on it, I put over 300 on in 5 days, no difference. I took it to a different dealer yesterday and they told me they don't see anything wrong, no codes or lights. I'm really at a loss and loosing my mind here! If anyone could help me on a idle relearn or some idea why it's doing this would be so appreciated. Thank you

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Have a look through the information in this link to see if there is anything that looks like it could resolve the issue

 

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So it started and ran at about 500 rpms then you pushed the gas up to 1000, so its normal stuff. It did not sound like 200 rpms at all. Nor did the tach read 200 rpms.

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Actually I did not touch the pedal. It sometimes stays lower longer but in the video you see it drop, then go up a little, then up to the normal position. That was all on its own

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Update

Went to 3 different dealerships and none could find anything wrong despite the symptoms. No codes = no answer I guess. I asked to replace or take apart IACV but they told me it's inside the throttle body on this year and cannot be replaced or taken out. Next step is buying new Throttle Body from Lexus $1,500. That's my only hope I guess since this car all the sensors are built in the throttle body and you have to replace the entire TB!

Wow I can't believe this

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A little update. I took apart the throttle body, cleaned everything. Everything looked good but cleaned it. After I put it back on, reconnected battery, and started it. Idle screamed at 2k rpm and would not go down. Had to shut off and restart a few times to get idle down. Problem still there.

 

I replaced the Idle Air Control Moter with a new one, no difference. I am thinking throttle position sensor next? I am going to do that before I buy a whole new Throttle Body. I'm hoping it's not the computer. 

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I had the exact same issues as your original post.  The car performed beautifully otherwise, but would consistently idle at 400 rpm with the AC off and the lights off.  With either the AC or the lights on the idle would be about 650 or so.  I lived with this for several years.  You can adjust the idle by moving a sensor at the front of the engine.  

Remove the engine cover

D2FEC93D-178D-4ADF-A58D-47E9F924C8DC_zps

 

Cover removed

399483F2-826D-4B12-9960-3458A4A7F7A4_zps

It's dusty - sorry!

Go to the front of the engine.

780BF145-C6C0-4BAA-991C-3F7E9DB82273_zps

 

Where my Philips screwdriver is pointed towards is a sensor locked down by two brass screws.

029B8579-579F-46A0-81AD-42E698CA74EC_zps

It's on the intake, and just underneath the electrical connector with the pink/purple wires.  It's not easily visible, but you can see it if you'll go to the driver's side (from where I took this pic).

F2403AA6-D434-4B7D-96EB-2AB471D00CCF_zps

 

You can see one of the brass screws here, just underneath the green wire.  The tip of my screwdriver is resting on the screw to which I am referring.  There is another screw about 11:00 that I was unable to get a good picture of while using my iPad.  It's on the other side of the sensor, about an 1.5 inches from the one I was able to get a pic of.  These are soft - do NOT strip the screws.  I fitted a couple screw drivers until I found one that fit precisely with no play between the screw slots and the driver head.  Then I used a lot of pressure forward, pushing the screw against the sensor before I began turning the screwdriver.  

Warm up the engine.  Do NOT remove the screws, but rather loosen them just slightly.  By moving the body of the sensor (twisting counter clockwise or clockwise) you will raise or lower the idle speed.  A little goes a LONG way.  As in just a little pressure on the sensor will raise the idle a few hundred rpm.  The adjustment range can be 0 to 2800 rpm.  I tried my best to get the idle set at 650, but when I would tighten the screws, I would raise the idle 50 to 75 rpm.  I finally left it at 700 rpm.  The idle is smooth, but I do notice the gauge could be between 650 and 750 rpm when I come to a stop.  I'm very happy with the results.

Post up if you have further questions.  

Micah

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The two screws may not be brass, but they felt soft. 

Also of note - I had a very irratic idle when I reconnected the battery after having done some work to the car.  The computer was gunning the throttle.  Kind of like what they do before a race on a Fast and Furious movie.  Adjusting this sensor brought the idle back in line and I set it back about 700 rpm again, which was as close to spec as I could get it.

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Hmmm...

Not sure how to fix that.  The pics are on Photobucket, and I used direct links.  I can copy the web address and paste it here?

Micah

Edit:  I changed the privacy settings on the folder where the pictures are saved.  It was set to 'private,' and I changed it to 'public'.  Hopefully, you can see the pictures now.

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Hello all and sorry for the long absence. I have a few updates, yea I know better late than never lol. 

As for the idle issue, I had to properly adjust the TPS and tweak it right for the idle, especially since I replaced the sensor and is VERY sensitive. So that was the issue.

 

Now for the bad news and the reason why for my absence. About a month after I fixed my problem and was sure it was gone, I got hit head on and the Lexus was totaled, I was devastated as it was a 99 with under 100k miles and no rust. Luckily I was not hurt, physically, emotionally yes. 

Now for my return, I’m back with a 98 Ls 400 and will be posting and commenting on here more. 

3C285F11-9718-4207-AF1E-BFE0D9EC045E.jpeg

C78B431F-9484-4428-9542-5F2ED75AD34A.jpeg

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Sorry to hear about the accident but I'm glad that your ok. Also congrats on the new to you 98.

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