hassanfuj

Hi.Everyone.

I have a ls-400 since last 8 years. It was running fine with no problems at all but then i had to change the engine because of the crucial oil leaks. Now i have a big problem. In the morning it starts fine but at very low rpm so i have to press the accelerator at a bit to warm it up. After that after driving for 10-15 kms to my office when i stop the engine and after sometime if i restarts it the car's idle speed starts rolling up and down( after every 2-3 seconds up and down, up and down) and it doesnot go normal so when i go back home in the same condition the car' s speed continues doing this while on the road, just when like cruise control is working on. (in this condition i am not even pressing the accelerator)This becomes dangerous when i have to stop on the red light the acceleration at that time is alway too high and i have problem hitting brakes and by the time when i reach home the engine becomes very hot.
The mechanic is on vacations now and his helpers doesnot know how to fix the problem. By the way the engine is replaced but the mechanic used the same old computer instead of fixing the one which came with the new engine. i donot want to go to the other mechanics as he had given me the warranty for 3 months)
The other problem is that my gauge is without back light and totally dark exept all the lights like oil, engime or ggear and seatbelts are working fine but the display is totally dark so i cannot see the speed or temperature guage or tachometer and fuel guage. some time the lights flicker but donot lit up properly.
Sorry for my poor english but please help me and i would appreciate if you donot ask questions that are beyond my understanding because i have very low technical know how. Just give me suggestion.
Thanks and regards

LScowboyLS

this problem is normally one of four things:

● wrong computer (ECU) for your year model - please verify that new ECU and old ECU have the same part number - the part number is the 10 digit number that begins with 89661

● failing ECU capacitors

● failing Idle Air Control valve (1997 and earlier models) - usually the bearings inside have failed

● a large vacuum leak in the system


ECU removal:

always disconnect the negative battery cable before disconnecting or reconnecting an ECU
beware: there is at least one hidden bolt inside the lower glove box behind a secret panel (not joking about this) the diagram below will help, but it can be a little tricky to get the lower glove box out the first time, just keep at it, and you eventually will locate all of the fasteners

Attachment 498614

hassanfuj

Thanks for the quick reply.
Have already read your highly informative thread about the ecu capacitors and will have them checked.
2ndly can you show by pictures that where is the computer located.
thirdly regarding failing Idle Air Control valve. where it is located and what does it look like and what do you mean by a leak in vaccum. i shall be highly obliged If you could explain the other 3 points by pictures like you did in explaining the ecu

Thanks and sincere regards.

LScowboyLS

in the diagram above, the computer, which we will refer to as the ECU in order to keep it simple, is labeled ECM and also shown as ECM Assembly

to explain more, I need the year model of your LS400

hassanfuj

oh sorry i forgot the most important thing it is the 1991 ls-400 ultra the japanese domestic model converted from right to left.

so it means that the ecu is The computer which is also called the ecm. ok got it.
what about the idle air control valve where is it.

thanks and regards

LScowboyLS

LScowboyLS

Idle Control Valve test procedure

hassanfuj

Thank you cowboy, thank you. I changed my ecu and the speed issues were solved but now after so many months I have another problem now after running for 10, 15 kms. when I stop at the traffic signal or some where. The car will not move even the car is in drive mode or reverse gear is engaged. if I accelerate only the engine will accelerate but the car will not move. Even the AC is working but the car will not move. so when I switch off the engine and after some seconds start again it will move a little with pressing the pedal to full so that I could at least drive it to roadside and park safely. And after giving it to rest for one or two hours it will move again but will stop again after 5, 10 kms.

And yes after changing the ecu the dashboard gauge meter was never had backlights.

hassanfuj

Hi anyone please help. I am still waiting. Cowboy?

dicer

Either the ecu has the capacitor problems, or shift solenoids. If its temperature related even transmission seal rings etc. You need to check transmission pressures and go from there. Actually it sounds more internal fluid leakage than electrical, it doesn't like warm fluid right?

Gene01

Is the ATF level correct on the dipstick?