I reopen this topic because the battery of my LS400 98 gets discharged if I don't run the car for about 10 days.
I measured the drain about 0.4V (7 V through 22 Ohm) which is a lot (10Ah/day, 100Ah/10days ok).
I tried to locate the draw by removing each (small) fuse one after the other -> no success. I have also disconnect without success one after the other the cable connections of the fusible Link Block close to Engine Room J/B..
As far understand the Body Ecu circuit is the only suspect which remains and indeed it is active when switched off.
So the next test is to disconnect the Body Ecu.
Hmm, it is located behind the Instrument Panel J/B (left foot driver). I would appreciate your feed back: Is that ecu easy to remove?, Have you experienced such a drain?.
Behind this issue, every system of this car works alright. I have cleared the the side of the butterfly throttle, I did not replace the throttle gasket because the one I bought from Lexus was not the good one (no much play to take this throttle body out). I have checked the spark plug. They are Denso Iridium, probably genuine from the factory (the car is 150 mkm), with the gap still at 1.1 mm. Replacement is to be done at 150mkm or when the gap is 1.2mm.