98 Ls400 Low Idle Dies When Warm Except W Ac On

[gp2m]

1998 LS400 110k mi.

Starts and runs fine when cold.

Once warm, idles too low, 300-400 RPM, and will die unless either I give it some gas or turn the AC on. No CEL.

Can someone give me some ideas. When I search for my symptoms, I'm just seeing solutions for 1st gen LS400 with the IACV problem. I'm not sure if this one has one or where it is.

Thanks for any input!

[McSwine]

1998 LS400 110k mi.

Starts and runs fine when cold.

Once warm, idles too low, 300-400 RPM, and will die unless either I give it some gas or turn the AC on. No CEL.

Can someone give me some ideas. When I search for my symptoms, I'm just seeing solutions for 1st gen LS400 with the IACV problem. I'm not sure if this one has one or where it is.

Thanks for any input!

Wish I knew...my 2000 does the same thing.

[curiousB]

Might be either or both:

1) Deposits inside IACV and valve not moving freely

2) Deposits in throttle body

Its a bit of work to clean these but its all time and little in supplies. Even if this isn;t the problem this is a good thing to do on older cars as routine maintenance so your time won't be wasted.

[Banshee365]

I'm with CuriousB... Clean the TB first and try it. If the problem remains clean the IACV. If you remove the TB to clean plan on replacing the gasket, mine didn't come off in one piece. Cleaning the TB is a very common procedure on the LS and usually owners rant and rave about the difference. However, some will also say it didn't make any difference but at least that would be done.

BTW turning on the A/C engages and idle-up circuit so that is normal. Some mask a low idle issue but running the A/C all of the time, I don't think that is how a Lexus owner should roll!

[gp2m]

I'm with CuriousB... Clean the TB first and try it. If the problem remains clean the IACV. If you remove the TB to clean plan on replacing the gasket, mine didn't come off in one piece. Cleaning the TB is a very common procedure on the LS and usually owners rant and rave about the difference. However, some will also say it didn't make any difference but at least that would be done.

BTW turning on the A/C engages and idle-up circuit so that is normal. Some mask a low idle issue but running the A/C all of the time, I don't think that is how a Lexus owner should roll!

OK Thanks.

Where is the IACV on a 98+ ? Can someone point me to a pic or diagram?

Thanks!

[steve2006]

Looking at the front of the engine with the engine cover removed you will see the intake plenum chamber right on top of the engine.

Mounted on the front of this with 3 nuts is the IAC valve.

Below is a picture of the earlier engine but the position on yours is similar

[gp2m]

Bottom center of pic or top left?

[ravig292]

had the same problem on my 2000 Ls.

it was the fuel pump.

[curiousB]

had the same problem on my 2000 Ls.

it was the fuel pump.

Doesn't seem like a fuel pump symptom. A fuel pump would tend to exhibit loss of power at heavy engine load not at idle...

[gp2m]

I've removed the TB and cleaned it. I do not see anything that looks like an IACV.

I'm beginning to think it doesn't have one.

Here what I have.

Someone familiar with the 98+ VVTI please point out where, if any, the IACV is located.

Thanks!

[blake918]

I'm beginning to think it doesn't have one.

It does, but not one that looks like the ones on the 90-97. The pics of the old iacv always seem to get posted when discussing the 98-00, but this is what you actually have...

PDFs: http://us.lexusownersclub.com/forums/index...st&p=397146

Real life shot: http://us.lexusownersclub.com/forums/index...st&p=397659

Without a/c mine will idle at 400 rpms too. It drives me crazy, and I still haven't gotten used to it after all these years. I think this is an electronic problem with a computer. If my local dealership was a little more competent, I'd consider trying to explain this to them, but it'd probably be a waste of time.

[gp2m]

Thanks Blake. That explains why I don't seet it.

I'll have to think about whether I want to take the intake manifold off. Driving with the AC on doens't sound so bad.

Is there a Lexus tech in Dallas who wants some side work?

[cardona6569]

Hi:

I guess our answer is to get a new IACV about a 700.00 part and see if it fixes it. Or clean the whole area really good that should improve it somewhat. Also the low idle tends to happen when the days are hotter if you notice in colder days it stays right on the money, but since yours sometimes shuts off, you might want to check your fuel filter and air filters. Mine can be at 400 rpms but doesn't cut off. If you never changed fuel filter do it, you do not want clogged inyectors or a bad pump in the future. As a last resort you might want to check the TPS and related parts but that should be done by profesionals, sometimes the tps wears out and causes problems like yours that the car shuts off. Seafoam it also it helps. Do not listen to opinion that you need a new TB unless you get empirical evidence of this component fault. We all have complained about the IACV but everyones lives with it without changing it, which may be the cure since more or less all of them have over a 100,000 miles or ten or more years of wear tear and sometimes old dirt. It might be as simple as a gasket in that valve failing and air escaping. Make sure you clean that TB and the tubes compartments in the close area. Also check the rubber hosing under that plastic Lexus cover they crack.

Cris

[McSwine]

I agree with the dude that thinks it's electronic related. I did some checking on this a while back and it seems a few folks with '98-2000 models got rebuilt ECM's or computers (or whatever it's called) and this fixed it.