jayjw

I posted this message in a different thread. I think it could help a lot of people with low idle speed problem. So I start this new thread.

My car is 1994 LS400.

The low idle speed problem is so common among the earlier LS400s. It is very difficult to pin point the problem. I have experiencing the low idle speed problem for about 6 months. Whenever the car stops at traffic light or stop signs, the idle speed was very low, sometimes it was below 200. With AC on it was a bit better. There was a strange symptom, when the air humidity was high like raining, the problem went away. I did quite a lot of study on this forum about this problem. There are many many LS400s having this problem. And people did all kind of things trying to fix it, cleaning the throttle body, replace or adjust the throttle position sensor, clean the idle speed control vavle, etc. but still having the problems.


There is one article giving me a lot of hint. Here is the URL.

http://www.autoshop101.com/forms/h21.pdf

It is talking about the engine air intaking. In it, it mentioned the "Power Steering Idle Up". In short, the power steering draw quite a lot of horse power from engine at low speed. To compensate this power, it use the "Power Steering Idle Up". Basically it is a valve, it opens when the car is moving at very low speed or idling. It gives addtional air to the engine and keeps the idling up. The LS400 has this valve. If you open your car hood, you will see a thin hose from the air intake (right after the Mas Air Sensor) goes to the power steering pump, and another hose gose from power steering pump to the engine air intake, right above the Idle Control Valve. After many years, this valve stops working. It stops giving the addtional air to the engine. And I think it is the LS400 engine ECU programming flaw, when the engine runs at low idle speed, it is only programmed to control the Idle Speed Control Valve in addtion to the power steering idle up valve. It is not programmed smart enough to detect the low idle speed below 650, and to let the Idle Speed Control Valve to give enough air to raise the idle speed to 650. In short, the ECU can not handle the situation when the power steering idle up vavle stopped working.

The above is my analysis after the studying.

To fix the low idle speed is really simple. Just to re-connect the two hose I mentioned above ( one hose from the air intake (right after the Mas Air Sensor) goes to the power steering pump, and another hose gose from power steering pump to the engine air intake, right above the Idle Control Valve).

Here is the steps to solve your low idle speed problem. Refer to the attached picture.

1. Disconnect "hose1" from "nibbles1".

2. Disconnect "hose2" from the Power Steering Pump Idle up valve (this end of hose2 is not shown in the picture).

3. Connect "hose1" (the side just disconnected from "nibbles1") to the Power Steering Pump Idle Up valve ("hose2" just disconnected from it).

4. Connect "hose2" (the side just disconnected from the Power Steering Idle Up valve) to "nibbles1".


It is pretty difficult to disconnect and connect the hoses to to power steering idle up valve because there is not much room down there. What I did was removing the air filter housing, it will give you some extra room to work there.

After I did this, the low idle speed problem went away. Man, do I feel good every time when I see the speed right at 650 in front traffic lights? You bet.

You may ask some questions, does this cause any problem when this hose keeps sending air to engine all the time? I think no. Just think it is equivalent to your gas peddle, it simply give the engine a little bit more air when you drive at high speed, or you can think you lift your gas peddle a tiny bit since this hose give some addtional air. But I can bet you won't feel any difference. When the car moves at low speed, the hose suppose to open, so there is no difference here. Also this hose is right after the Mass
Air Sensor, so it won't cause any unmeasured air issue.

There is an addtional benifit by doing this. The LS400 also has a known problem, leaking Power Steering Fluid to the engin intake. The problem of that is also caused by the Power Steering Idle Up valve. By loop it back, you prevented this future problem.

I think the Toyora engineers should totally eliminate the Power Steering Idle Up valve. Instead, they should use the ECU to detect the low speed and sending the addtional air through Idle Speed Control Valve.

lexusnutt

Jay,

Good job! This may be possibly a great solution which I haven't tried yet, but I know there are hundreds of owners out there who are experiencing this problem.

I hope it alright with you if I posted this on another board (us.lexusownersclub.com). I gave you full credit!

(Moderator, if this proves to be a valid fix by a consensus of the members on the board, can we add this as a sticky?)

Cheers!

jayjw

Lexusnutt,

Thanks.

Please post it wherever you want if it can help the LS400 owners having the same problem. I would be feeling honored if you do that.

Thanks again for the good word.

crazimofo

any feedback of people trying it?
need some results..

post it up here asap..
will get to it as well...

props to jayjw! ! !

deelite_00

My car just started to do that now. If I leave it the way it is and not do anything about it, would it damage anything? Any side effects?

Thanks

jayjw

deelite,

I don't think it will damage anything if you leave the way it is. The problem might be just getting worse with time. You may experience engine stops once a while. It is just very anoying.

jbruntlett

I tried this "fix" by connecting nipples1 and nipples2 together with a new hose and hoses 1 and 2 with a tube connector. The idle speed was raised, and I was able to travel 800 miles without the engine stalling. The downside was that the idle speed was also raised all the time and almost caused my wife to collide with other vehicles in icy parking lots because it went too fast with her foot off the accellerator, and braking caused skidding. My ecu will be replaced next week for a more permanent solution. My car is a 1995 LS400 with 207,000 miles with the stalling problem occuring periodically for over a year now. Most recently was a stall in rush hour traffic, in an inside lane in Bellevue, Washington, which I consider to be a safety issue, rather than the driveabiliy response of Lexus. Luckily, I did not have an accident and this fix allowed my to keep driving the car until the ecu could be replaced.

crazimofo

Yeah its not a permanent fix, but rather a temp. solution.

jbruntlett keep us posted on the ecu being replaced after you do it?

thanks its greatly appreciated.

welcome to clublexus forums! stay a while!

deelite_00

Thanks for the info jayjw.. much appreciate it.

Kinda sucks since my car has only 73K miles on it. There was a thread I saw here that someone took out the Idle Control Valve and messed with the spring/magnect inside and then reinstalled it. They said the idle went back to normal again. i'll try to find it and let you guys read it for comments.

deelite_00

Here is the thread I was talking about. It pretty much relates to the problems we are having here. Any comments?..

https://www.clublexus.com/forums/sho...highlight=idle

jayjw

jbruntlett ,

I don't know why your car idle speed raised too much. The power steering idle up valve suppose to open when you car runs at low speed, which equivalent to your connect nibbles 1 and 2. So there is shouldn't be any difference when the car runs at low speed. Also, the idle speed should be right around 650 when your car stops.

I have my car fixed this way for almost three months, it runs perfectly.

harjp

This is an interesting thread. jayjw, is your car still doing well with this fix?

One thing occurs to me: in addition to by-passing the power steering idle up valve, this "fix" also by passes the idle air control valve because you are now supplying a direct line of air to the engine all the time. So this might fix a low idle problem when the idle air control valve is bad.

By the way, according to the tech manual you link to, the power steering idle-up valve is supposed to open only when the steering wheel is turned all the way left or right (see pg. 12). So a bad power steering idle-up valve would only produce a problem when the steering is turned to one stop or the other.

I'm also wondering where "hose 1" originally goes to, before you did your fix. To the A/C idle up maybe?

jayjw

harjp,

Sorry for the late response. I haven't got to this site for a long time.

Since I did the power steering idle-up valve in May 2006, I never had any low idle speed problems up to today.

This fix does not by pass the idle air control vale. It is just to add additional air on top of the idle air control valve. The power steering idle-up valve is now constantly open.

Jay.

ryanSC300lover

iTrader: (1)

My car seemed like it had low idle, but it never stalls or anything, runs fine.

But after reading this thread, it says 650 is normal. Which mark is "650" on the tach? I will check it in the morning, and post pic of my idle.

ryanSC300lover

iTrader: (1)

Ok car is idling at the 2nd mark from 0. There are 4 marks between 0 and 1.