crazimofo

is a 1991 LS400 ECU/ECM compatiable on a 1990 LS400?
or what years are compatiable with each other? california models are compatiable or whats the difference?

please let me know
i suspect a ecu problem..


posted from another lexus site model differs however same exact problem:

I am trying to make a thread here for the many of those with low idle, engine quits after an extended highway cruise when coming to a stop, and a mysterious drivetrain jerk when you let off the throttle and get back on....sometimes...and usually happening over 40 mph.

My 95 Ls400 built april of 95 which now has 150,000 miles has these problems.
I've done full diagnostics. I've gone after the throttle body and the Idle control valve. All of which were working perfectly. After 3 days of reading threads at several different forums of similar problems with 95's, several emails and follow ups on who found what the problem was and how solved I wanted to put all the information here so the next guy could find it easier.
Some guys are driving around with the a/c on to keep the engine running at a faster idle to keep the car from dying.

I'm convinced all 3 problems are related to the ECM and it's controlling of the idle air control. While there were a couple of TSB's on this it was never a recall. Those of us who bought used or have high miles are out of luck for any dealer help...at least I would think.

Your Ecm is located behind the glovebox on the passenger side. If you want to read what number Ecm you have..you can do that by not removing it. Just remove the lower plastic panel below the glovebox and look up in there. You'll see "Engine Computer Label" and the numbers.

For 1995's:
Your original Ecm is either:
89661-50220 or 89661-50221 if Federal (49 state). Lexus new replacement on the TSB says to replace with 89661-50224

If California then your orginal Ecm is either 89661-50230 or 89661-50231. The TSB calls for 89661-50234
But searching a local Lexus parts site shows that number has been replaced with 89661-50235-85.

The cost of these Ecm's new is just total crazy. But there might be another solution.
One member bought a used pcm from a wrecking yard #80661-50224. He paid about $150 for it and it solved his issues. I did some searching in wrecking yards and there are some of these #'s out there.

If you have a California car then there seems to be few out there. Mine is a California car. I don't know if a 49 state Ecm will work...I suspect it will...but unknown at this time.

Another member bought a remanufactured Ecm for his 49 state car. He paid $300. for it and it has a 1 year warranty. He also stated that it cured all problems. The company he purchased it from was Auto & Truck Electronics in West Palm beach, Florida. He said the part number was #95 Int 56834. (That was a 49 state unit).


Need some feedback please..
thanks
.

NewLSlover

I believe my 93 is doing this same ****! But first, I'll clean my throttle body and check the IAC. But I notice I have to ride with my A/C at least MED or my car will stall randomly when I come to a stop. I, too, have the infamous drivetrain jerk around 40...hmmm.....

crazimofo

hahaha..sucks yeah..i know this is common..friend of mine has same problem..who else got this problem, we go to figure it out..
cleaned throttle body about 10k ago...a definent must...
i however did not touch the idle air control valve..i too have to ride with my a/c on or car might stop...drivetrain few times not often....

can you use a 1991 ECU on a 1990 LS400 or what are the compatabilities of the different ECU's...
does it matter if it has air suspension or springs/struts?..traction or no traction?..?

NewLSlover we got to solve this...im leaning towards the ECU..although might be the IAC....
do you have any check engine lights or codes?
do you smell catalytic converter smell going bad? like rotten eggs?
thanks

NewLSlover

Well...I don't have traction...and I don't have air suspension.

I DO, however, get CEL when the car stalls...but it only stays there until I restart the car, then it's gone.

It pisses me off though, because it's SO DAMN random!

I don't smell that catalytic converter smell either....hmm, this is odd.

And, do you notice the onset of stiff steering just before a stall?

crazimofo

quoting NewLSlover:
I DO, however, get CEL when the car stalls...but it only stays there until I restart the car, then it's gone.And, do you notice the onset of stiff steering just before a stall?

this is normal to happen before the car shuts off with the key still in the ignition and on the on position or start.

happens at random too.mostly after highway trips coming to a stop.
drops idle low like 200=400 RPM sometimes..just raise the idle by pressing the gas and just continue driving along..turn a/c on rasies idle little bit...low idle causes a lot of vibration..then sometimes it just dies out.

yeah the catalytic converter problem is not relevant, was just curious..

BTW, also got brand new MAF sensor on it too..weed that out of possibilites.
i have 1 brand new ignition coil too.

what about your O2 sensors? when did you change that?
do you have an EGR pipe crack or something sounding like a small exhaust leak coming from the back of the engine close to the engine bay or firewall?

another member told me it might be ignition coils...i weeded that out..



thanks for the feedback on it though...

did you check your IAC valve?
let me know if you do..

Brandicus

iTrader: (6)

i have a 93 as well and i dont have the 40 mph jerk. however if i turn the air off the auto function the car will sometimes stall at very low speeds, might not be related...

btw the car has never stalled with the auto function on

crazimofo

Brandicus did you fix the problem or do you as well still have it...
I think its related because I too don't have that 40mph jerk, kind of rare for it to happen to me but experienced it a few times.

Och

iTrader: (3)

I fixed my stalling problems by removing and completely cleaning out the throttle body.. its a 94 ls

crazimofo

anybody else had this problem and how did you get it fixed?
we need to find a common solution to all this..

jayjw

I had both problems. My car is 1994 LS400. Here is what I did and both of them fixed.

The drivetrain jerk around 40M/h speed. I had the problem two years ago. It happend almost every time when I drove the car around 40M/h and lift the gas peddle a bit. The root cause of this is the transmission fluid. After I flushed the transmission fluid with Toyora Type IV, the problem was totally gone. Never came back. You either have it flushed by a dealer, or do it yourself.

Here is a link show you how to do it. http://www.lexls.com/tutorials/trans...ransflush.html

The second problem, low idle speed is a tough one, but easy to fix. I just fixed it last week. 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 what you need to do. Take one hose to loop back the power steering pump idle up valve, simple disable the valve. Take the other hose, one side connect to the connector right after the Mass Air Sensor, the other side connect to the connector to the engine intake right above the Idle Speed Control Valve. In other words, you keep this hose always open. It always give the addtional air to the engine.

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 opening 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.

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.

Och

iTrader: (3)

Jay, before I cleaned my throttle body, I tried doing exactly what you described, and it did resolve the problem, BUT this is not the correct solution. While it works, it does allow for unmeasured air to enter the engine, because essentially you are creating a "leak" in the intake.

But then again, this thin hose isnt really leaking too much air into the intake to cause any problems. So this is a very good temporary solution.

jayjw

Och,

I thought about that too before I did it. I was concerned about the unmeasured air leaked to the engine. But The power steering idle up hose is right after the Mass Air Sensor. So the air through this thin hose is also measured by the sensor. If you look at the LS400 air intake, all air goes to the engine is measured. There is absolutely no hose connected to the engine intake before the Mass Air Sensor.

NewLSlover

Hmm..now that I think about it one of my hoses that you speak of (dunno right now) snapped off the nipple it attaches to on the air intake pipe...The whole little nipple it was on snapped off inside the hose...Lexus said it would be some ungodly ammount of money to fix..maybe this is causing my random stalling?

Och

iTrader: (3)

Maybe I'm not understanding your post correctly, but this is what I did before I cleaned the trottle body. I disconnected the thing little hose from the ICV valve, as shown in the picture below, and that alone resolved the low idle issue. I was considering capping the ICV valved, and using a coupler to connect this hose to the thicker hose coming out of the intake, to avoid unmeasured air, but then I just said screw it, and cleaned the throttle body, and that did it.

In fact, before I cleaned my throttle body, the idle was low, and whenever I would switch from a gear into neutral or park, the RPMs would fall drastically, and the slowly raise, but sometimes the car would stall. Well now the RPMs actually raise when I switch to neutral or park.

Och

iTrader: (3)

On that picture, can you point out which hose that is?