sam6918

Hello and thank you for reading...

I had a previous problem with my LS400, It was not starting due to no spark. Well i FINALLY got that fixed and it turned out to be my crank poss sensor. After the repair my previous PROBLEM started again. The car would shut off when i come to a stop unless i keep my foot on the gas pedal. If i remove my Foot, the RPM would go down to ONE notch above the ZERO then stall. keep in mind this only happens after the car has been running for over a hour. Today i went to start the car it cranked but would not start. I had the Battery, Alternator, and Starter checked all was good. But when the car started giving me the problem of stalling when i come to a stop i drove it back to Auto Zone and had all three checked again. They said i had a BAD Alternator. (does not make since because the car starts everyday if the alternator was bad i would have to jump it every time i start it and the car would not have gotten me far) its been 2 weeks since they said i had a bad Alternator yet the car still started everyday and has power (expect for today)

LScowboyLS

normally on your year of LS400, when you have problems stalling after an extended period of running, the most likely two suspects, in order of likelihood are:

● Idle Speed Control Valve (bearings often go bad)

if the bearings are indeed bad, I can point you to where to get a good deal on the real OEM Japanese bearings


● failing ECU capacitors

sam6918

how do i test the idle speed and how do i test to see if the ECU is failing? Thank you

LScowboyLS

follow that link above for Idle Speed Control Valve test

for ECU capacitors, you can do a visual inspection and/or do Yamae's ECU ripple test

Yamae

Did you use a good genuine crank position sensor after cleaning the other side which is the rotating tooth side?
I have experienced several similar problems that happen after engines were fully warmed up. Many of those were caused by the failed or non genuine crank position sensors. As I observe the waveform of the them using an oscilloscope, some of them became weaker and others had unusual waveforms when temperature became higher. Position sensors usually use a http://en.wikipedia.org/wiki/Hall_effect_sensor or a http://en.wikipedia.org/wiki/Magnetometer and a small piece of magnet is in it. These have a thermal point called http://en.wikipedia.org/wiki/Curie_temperaturehtml and the functionality is quite temperature related. Genuine sensors are quite reliable but some of aftermarket ones are not always so. Also sensors do not work well when the other side is clogged especially with the small metal particles.

I suggest you to check and compare the waveform when engine is not warm and warm enough.

sam6918

Thank You very much i will check them tomorrow as it is dark outside now and very cold here in Michigan. I will let you know what i find.

sam6918

Thank you very much. I am gonna do Further testing on it tomorrow I will first check what LSCOWBOYLS told me to check and if that is not the problem i will return the car to the repair shop where they had changed the sensor and i will have them test the waveform as the sensor/labor are still under warranty. I will Post a reply to let when the problem is fixed and note what the problem was

LScowboyLS

actually check what Yamae recommended first, he is the supreme LS400 guru!