1993 LS400 Idle / AFM

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Hello everyone,

my name is Martin and I am from Germany, reading on this Forum for quite a while, I decided to get active due to a tech. Problem on my LS400, I hope there is some help here as this seems to be the most qualified Forum, great!

Problem is as follows.
On a big service on my car I made the ultimate 'beginner's mistake' and tried to clean the AFM, which killed it instantly. I got the error code 31, so spent 400 USD for a new AFM.

As the new AFM arrived, I assembled everything, but the CEL is still on with code 31, as I thought the new spare part could be faulty as well, I replaced it, but the replacement didn't change anything. Still CEL on with code 31, rough idle and stalling engine when warm. I checked all the wires from the AFM wiring to the ECU, everything fine, the two brown cables have proper ground, the blue cable is connected correctly to the TPS. The AFM itself is in spec by measuring the resistance according the workshop manual.

I checked also the Idle control valve, which is working fine, as well as the TPS. But they would cause another error code, right? Searched also for vacuum leaks, all hoses and connections OK.

To be honest, I am at the end of my knowledge, so help is very appreciated.

Many thanks for your answers in advance and best regards,

Martin.
 
Last edited:
Hello,
Thanks for your reply, I disconnected the battery for several times, also overnight. It didn't help unfortunately, after starting the engine the CEL comes back on every time.
Best regards.

Martin.
 
Hi,
I checked the ECU, all capacitors looking fine.
Also checked the ECU Temperature sensor, it is within spec.
Best,
Martin.
 
Do you have access to a scan tool to monitor live data?

About half the ECU's I swap out have visible leakage from the caps. It's nice when the damage is visible although I often see leaking caps and it's not the issue but it would be shortly if I left them. I'm quite lucky as I generally have a known good ECU to swap in.
 
Hi Gloverman,

I have a small Oscilloscope and a Multimter with a Hertz - Meter.

Yesterday I spent half a day tracking down all wires from the engine compartment to the ECU and to other elctronic parts such as the TPS, ICV, no Error on non - Continuance at all.

Could it be that the second replacement AMF is erratic as well? Is there a way to check the AFM, as the workshop manual just checks the Inlet temperature sensor (THA-E2)
In my eyes only two options left: AMF#2 or the ECU.
I have bought the low-ESR - Caps for my ECU already, just in case I will need them, it seems that it won't be a mistake to swap them now...
But: Could a bad ECU show up out of nothing, just by doing a service on the car, what are your experiences? I have just one and always the same CEL Error on my Car: Code 31 - AFM.
Unfortunately Parts are very hard to get here in Europe, Lexus stores them just 10 Years and you won't find anything on ebay, etc.
Best regards,
Martin.
 
Just doing a service shouldn't cause any issues but doing a service with something else happening can and then there's shit happens. Haha.

AFM fault codes can also indicate air leaks either in the intake to the Tb or Iac or post Tb in the air surge or manifold.

I monitor the frequency of the afm along with the air volume using a scan tool to give an indication of afm function or fit a known good one. Pretty much all I do at the moment is UZ repairs and wiring so I've built up a few spares.
 
gloverman said:
Just doing a service shouldn't cause any issues but doing a service with something else happening can and then there's shit happens. Haha.

AFM fault codes can also indicate air leaks either in the intake to the Tb or Iac or post Tb in the air surge or manifold.

I monitor the frequency of the afm along with the air volume using a scan tool to give an indication of afm function or fit a known good one. Pretty much all I do at the moment is UZ repairs and wiring so I've built up a few spares.
Click to expand...
 
Hi,
You are absolutely right..! I will never touch an AFM again.:)
I will search again for air leaks in the areas you described. Do you have a safe method finding them? I use break cleaner and spray the parts I 'test'.
Between which ports are you measuring the frequency, what shows you a good afm?
Many thanks for your input.
Nevertheless I will get my ECU up to datebwith new caps and try to get a new one.
Unfortunately you are too far away. Are you selling spare parts as well?
Best regards!
Martin.
 
For air leaks I have a smoke machine. It produces a couple of psi of smoke which I flow into the suspected area.
Brake clean can work well too.
I measure frequency with the scan tool. I can't remember the exact figures off the top of my head.
I do sell a few parts (haha). I have a lot of conversion parts and quite a few new and second hand stuff. My business is pretty much uz stuff.
 
Hi,
After I got back from work I did some more 'leakage research' - no air leaks found by spraying all the hoses and flanges one by one with break cleaner, but I realized that it does not make a difference if I pull out the big hose of the AFM or if is tight on the tb assembly. Also if leave the plug of the AFM on it or let it hang loose after pulling it does not make any difference, the engine is running rough and is surging and stalling after a while. I tested both, 1. With AFM connected, 2. without AFM connected.
As you sure have a big expertise, is it often happening that replacement AFM's are faulty??

I bought from this dealer in Germany: http://www.ebay.de/itm/Luftmassenme...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

I dont get rid of the expression that the second replacement AFM is faulty as well...

Best,

Martin.
 
This is what I am going to do, I ordered one in the US now. At the weeked a friend of mine, he works at a sattellite company and is a very good eclectronics specialist, is soldering in the new Caps for the ECU.
I will be on Vacation from this Friday on, but will keep on posting afterwards.
Hopefully it works - fingers crossed!
All the best until then.
 
Hello again,

back from vacation parts from US arrived, but no news at all, still the same problem.
As I am expecting now that the ECU is shot, I would appreciate a hint which ECU's are interchangeable, as I cannot find one with my original part number: 89661-50160, are there any other ECU's which will fit as well? (Pin - Layout is 34/22/16/28). For example I could get a -50140, or a -50150, or a 50142-84.
Many thanks in advance!
Martin.
 
Last edited:
I have interchanged 50170 in place of 160 without issue. The rule I work on is any ecu from the same year range - so late 92 through to mid 94 in the 10 series ls/celsior. They have the same header plug into the centre of the ecu with the wide body ecu.

Crowns in that year range (uzs141) have same header as early soarer 40/40/40 So you can't get that wrong. There is a later soarer which runs Alloy afm and shares a header plug and pinout with yours and will have a 24 chassis id on the ecu number. These are rare over here and I can't remember the number from memory. I've interchanged these as well successfully.

The last number doesn't matter. When the ecus get updates the count up so 50170 becomes 50171 and so on. I've never seen a 140 or 180 but should be ok.

When swapping if I'm not sure I just reference injector number and AFM. I know mostly which pinouts are different from memory. (Yes I wire the odd one or two haha)

Later 20 series have the same plugs with the header offset into the body and don't interchange. 50380 / 50240 / 50250.

There's also later crown which have 3A chassis code. Same header but smaller body. These interchange with 20 series so no good for 10. Different afm, sequential injection, different mrel location etc.

I'm pretty lucky as I think I have an option for nearly every ecu for 1uz in stock except 131 crown.
 
gloverman said:
I have interchanged 50170 in place of 160 without issue. The rule I work on is any ecu from the same year range - so late 92 through to mid 94 in the 10 series ls/celsior. They have the same header plug into the centre of the ecu with the wide body ecu.

Crowns in that year range (uzs141) have same header as early soarer 40/40/40 So you can't get that wrong. There is a later soarer which runs Alloy afm and shares a header plug and pinout with yours and will have a 24 chassis id on the ecu number. These are rare over here and I can't remember the number from memory. I've interchanged these as well successfully.

The last number doesn't matter. When the ecus get updates the count up so 50170 becomes 50171 and so on. I've never seen a 140 or 180 but should be ok.

When swapping if I'm not sure I just reference injector number and AFM. I know mostly which pinouts are different from memory. (Yes I wire the odd one or two haha)

Later 20 series have the same plugs with the header offset into the body and don't interchange. 50380 / 50240 / 50250.

There's also later crown which have 3A chassis code. Same header but smaller body. These interchange with 20 series so no good for 10. Different afm, sequential injection, different mrel location etc.

I'm pretty lucky as I think I have an option for nearly every ecu for 1uz in stock except 131 crown.
Click to expand...

Hi Gloverman,

Good to hear from you! :)

So now I know what I should look for. Many thanks!
If you have a spare part in stock which you consider to sell, I would also appreciate buying one from you! ;-)

Very best regards,

Martin.
 
Well the link for the last on is for a 2JZ so I dont recommend that one.

Does your car have EGR? Just thinking you have a general / Europe spec ECU and swapping in a USA spec may give EGR codes. I work with JDM stuff most of the time ut do see quite a number from overseas.

I'm not familar with the 50142-84 but by the specs it looks fine and the price isnt much more than the secondhand unit.

I have 89661-50170 which are rebuilt which sell for $500NZ (about 300 euro)

Good Luck.
 
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