Hi guys,
Having read this topic and having mentioned earlier that I had the same problem of the dying engine, I sent my car to the Lexus dealer, with a reference to this topic.
It seemed I already have the updated computer (ECU) in my '95 LS. So that couldnt be the problem. The dealer had an other possibility and that was to check the fuel related items in the car. Excuse me for my bad english (dont know the terms/right words) but I will try to make this clear
They found out that the fuelpump, some related sensors, the fuelfilter and other parts that are in relation to pumping fuel from the fueltank to the engine and "giving" fuel "back" to the fueltank were "very filthy". So they took apart all the related parts and cleaned them. The only thing they replaced was the fuelfilter for a new one.
So, good cleaning seemed to have solved the problem. Costs? One and a half hour labour (€ 120) and a new fuelfilter (€30).
I took the LS out for the trips at which the problem always came up and guess what...no problems any more! Nice idle at around 600, not less (was getting used to 300, 150, zero...)
I hope I made this solution clear, if not, just ask. Hopefully some of you can use this solution...
PS There were indications about this problem arising at mileages above 200000 km...well, considering that parts may be poluted after so much time/miles this may sound logical now.
Greets from Holland, Speedy J