LS400 periodically idles real low and will sometimes stall on stops

[rollinginmyLS400]

I have a 1992 LS400 with 135k miles on it. Just recently I started experiencing issues with my idle.

From what I understand, the LS400 should idle around 650 when in drive or parked, etc. Mine typically does. However, lately, sometimes it will idle around 400 or sometimes even lower, and it appears the car will stall and die at any time. It has actually died several times when coming to a stop sign or stop light recently, and then I have to re-start it and it is tough to keep it going.

I have read that the Idle Air Control Valve may be the culprit of this, especially if you see some blue smoke right on start up (I do) and if you are leaking Power Steering fluid (I do). The IACV is located right underneath the power steering pump from what I understand. But this is all off what I have read so far.

Has anyone else experienced this issue and what was the fix? Also, if it is my IACV, how hard is that to replace myself? I cannot seem to find any good info on how to replace your IACV. I am worried if I go to the Lexus dealer I will be paying hundreds of dollars to repair.

Any info would be very helpful. Thanks in advance!

 

[Warm Pudgy]

mine did the same thing for a while, it has gone away now

i didnt really do anything for it, the only treatment ive done for the car so far is lucas fuel injector cleaner

 

[V8sprint]

The IACV is in the frontside of the air intake plenum. Take it out and clean it and make sure it works.
The smoke you are seeing is likely ps fluid being burned into the intake plenum. There is a bypass valve below the p.steering resevoir-- this is what you are refering to being the IACV.. which is obviously incorrect.
The p.steering bypass valve allows power steering fluid to go through a tube into the air intake and burn off. It is completely unessesary and should be taken out and pluged, along with the tube nipple on the intake tube. This should eliminate the ps leaks and smoke at start up.

 

[rollinginmyLS400]

Thanks for the info on the Idle Air Control Valve. I had read somewhere else (cannot remember where) that the IACV, if it goes bad, can pull PS fluid into the intake causing PS fluid loss, which coincidently enough I experience also. So that is why I thought maybe the two problems were connected, but it appears they may not be.

As for the IACV, the idle issues I am having are more vital right now as the car is pretty much undriveable as it stalls out at every stop. It was an intermittent problem, but now it is pretty consistent.

The Idle Air Control Valve would control this, correct?

You said the IACV is located on the fronside of the air intake plenum. I do not have a LS400 repair manual, just the owners manual, so I am not quite sure where that would be located. And I admit, I am a rookie mechanic! Do you happen to have schematics on that or pics of where it would be located? Maybe purchasing an repair manual for the LS400 is the way to go, but they are pricey. Any other info you can provide on this issue is greatly appreciated!

 

[V8sprint]

Although stalling can be caused by several variables I would start with the IACV. There is alot of information about the IACV on this site if you search. Here are symptoms diagnosis http://lextreme.com/Lex DX.pdf

 

[rollinginmyLS400]

Update:

I took the IACV out of my LS400, and gave it a once over clean. The unit actually looked in beautiful shape, and nothing appeared to be frozen or gunked up. But I cleaned it anyways and put it back in the car.

Now my LS400, instead of idleing extremely low and stalling...is racing high. In fact, when in park, it the idle will jump between 1000 and 2000 rpm's constantly...up and down, up and down. When in drive, it is around 1200 rpm's and the car doesn't want to slow down when you brake because the idle is off.

So it would appear that my issue must be with the IACV. If it wasn't, I would have assumed the the symptoms I experienced before would have stayed the same, but now they have changed.

I am going to take off the IACV again and see if something stuck...a shot in the dark at this point.

Does anyone have any clue as to why the symptoms may have changed? Anything I can look at to repair the unit?

I have pretty much resolved to the fact that I most likely will have to pay the 400 plus dollars for a new IACV.

 

[V8sprint]

There is a procedure to test either continuity or resistance with the IACV. Also I may have an extra IACV or two around. PM me ill check for you.

 

[rollinginmyLS400]

V8sprint...I attempted to send you a PM but the site is saying you are not able to receive Private Messages. I had to set mine up to allow this in my profile, so maybe you need to do the same?

Anyhow, I would love to have you check on extra IACV's you may have.

As for the procedure to check continuity on the IACV, what is it? I am a rookie when it comes to car work, so I am not sure if it will be something I am able to do or not.

Thanks

 

[V8sprint]

I am certain now, I was thinking of the Throttle Position Sensor TPS about the testing.
Do you have any check engine lights CEL on?

 

[jeremy]

Here's the service manual info for the idle speed control and the throttle position sensor... Hope it helps.