ls400beave

So I have a 98 LS400 that is a great car. Need advice on the idle issue. The issue seems intermittent so I thought I would ask for some suggestions. The basic problem is a low idle 3000 to 4000 RPM's when the car is stopped in gear (and car vibrates a bit). But if you turn the A/C on the RPM's shoot up to 6000 to 8000 rpms. However, it does not happen all the time. When you run the car for the first time for the day it is fine. Runs right at 5000 to 6000 RPM's in gear when stopped. It is the second, third time you drive the car for the day. I have recently cleaned the throttle body and I just replaced the accelarator pedal sensor located on the throttle body. Can you adjust the idle? I really think that is one of the two TPS going bad. I just thought it would throw a error code. One TPS is traction and the other is fuel injection.. I think it is the fuel injection one. Also, I wonder if that would effect the cranking on starting the car. My car always has had a long crank time to start... Let me know if anyone had delt with a similar issue,

PureDrifter

iTrader: (10)

you mean x00 rpm right, not x000. if your car is idling over 800 or under 500 rpm warm then there's a bit of a problem...

when did you last do spark plugs? air filter is clean? mileage on the car?

you did clean the BACK of the throttle body/throttle flap right? the front is clean.
with the engine cover off and looking down at the throttle body, there's a small metal plate held on with 2 screws. take those off and clean the cavity out with some carb cleaner and an old toothbrush.

ls400beave

Thanks for your input... Car has 230,000 miles. I did clean back of the throttle body.. I am not sure when the plugs were changed last. It might be a good idea to change those. However, the car has always been maintained at the Lexus Dealership and had a complete inspection right before I bought it in March 2011. The odd part is it is not consistant. Most of the time it idles right at 500 RPMs in gear at stop (no A/C on). Typically the onl time it goes below 500 rpms's is after it has sat for a couple of hours and is driven for the second time in the day.. I am puzzled because it seems like a computer issue more then a mechanical issue.. I might just buy the TPS (fuel injection) sensor and see if that will correct the issue... Thanks again..

PureDrifter

iTrader: (10)

if you feel like throwing money at it feel free.

you never answered about cleaning the idle ports on the throttle body. (the panel i described)

kevwats01

iTrader: (5)

@ls400beave
Did u fix the problem?
My friends having the same issues.

Yamae

Recently I just have helped a friend of mine who own a 98 Celsior which had a low idle problem and a strange acceleration problem when he turned a corner. I mean the car did not accelerate as if the AT was not engaged. As he pushed the gas pedal more, the car suddenly accelerated and this was rather dangerous.

Those two problems were completely gone after cleaning the throttle body and the air mix path. I took photos at that time and I show you them here below. The air mix path is located at top of the throttle body. The red arrow at top left photo shows the location of the air mix path. 2 photos at right side show it and the lid for it. As PD wrote at former post, the lid is held with two screws.

There are 2 bigger holes and 8 smaller holes at the air mix path. Clean all the holes using a engine conditioner or a carb. cleaner. You need almost a whole can to clean those 2 bigger holes. The air mix path is designed to supply the air to injectors aiming to get better gas mileage mixing the gas and the air at the injector. This path is very important both for the mileage and the smooth acceleration.

I must tell you 2 more that the cleaning of the air mix path should be done while the engine is idling. The throttle body has to be cleaned removing hoses and you also need to push the pre-throttle valve manually.

LScowboyLS

be sure to wear a respirator or set up a giant fan or wait for a very windy day outside when cleaning throttle body, air mix path, etc. - Throttle body cleaner/carb cleaner causes cancer and brain damage due to very bad chemicals such as Toluene, Benzene, Methyl Ethyl Ketone, other ketones, Xylene, etc.

RugbyDad

Sorry to revive an old thread but I had recently cleaned my throttle body (still attached to the engine) and didn't really receive any pep from the throttle. Still felt like with a light foot, the engine wouldn't respond as quickly as I have noticed on many other cars.

I must admit, I totally neglected the air mix path. Just cleaned it 15 minutes ago. I did it wrong I'm sure (I broke the little gasket on there so I'll probably need to replace that soon. And I turned the engine on after I removed the air mix path plate but before cleaning it, needless to say, the engine didn't appreciate that too much and died soon after starting it when I sprayed throttle body cleaner into the air mix path).

Anyhoo, after cleaning the air mix path, that pep is back... mostly. It's not instantaneous response but it is noticeably better. And I believe I probably could've cleaned it better with a q-tip to get into those two little holes better. Matter of fact, I'm gonna go and re-clean it more thoroughly.

note - My idle is only low (400-500) when I first place it into drive from park (When driving and coming to a stop, idle is at ~650). Engine warm, no A/C is right around ~700. With A/C ~800. Engine cold 1000-1200. After doing my first cleaning of the air mix path, the idle has remained the same. Now to go clean it again, much MUCH more thoroughly.

PlatinumV8

To revive this thread again, I am going to do a complete tear down of this area and clean everything properly, with the engine off. I see no reason to risk ingesting chunks of debris into the cylinders.

Let me know if there is any sound reason to do this with the engine running.

I will post many pics and descriptions, so check back again for the complete write up.

I agree with Cowboy, but make sure your respirator has organic compound filter inserts, the cheap ones are for just suspended particulates, dust etc.

Debbie

JJDAG

Ok Ive been having these symptoms for a bit one of the things that was happening while backing up the car would lurch almost like I was driving a manual trans, That said I followed Yamae's instructions and cleaned the throttle body and removed the top plate and cleaned the air mix paths, I used up close to 2 Cans of CRC and a full can of Sea Foam spray. There is a noticeable increase in throttle response, when under full throttle it now accelerates fast and smooth, the lurch is gone in reverse and that bump when slowing to almost a stop then giving it the gas is gone as well. Thank you Yamae for sharing your knowledge and the how too pictures!!! To all other members on CL the advice given to us by the senior members is priceless. I have followed the instruction from several long time members on here and each time the advice was spot on and I saved a ton of money by simply doing what they said to do!

spuds

I just cleaned mine today for the every 2 year smog check.Hard to do with 6 inch spray nozzle to air mix path.So I ordered 2 50 inch spray can straws from ebay,should be awesome!!ORDER DATEMay 08, 2021 ORDER TOTALUS $12.92

2-Count FS250 FlexStraw Aerosol Can Replacement Neon Green 50" Party Tableware
(384096963915)ITEM PRICE:US $11.99