Location of map sensor in 1992 lexus ls400

SOURCE: 1992 sc300 lexus

it is under the vehicle, driver side, below the seating area, in front of the rear wheelwell, mounted on chassis in fuel line.

SOURCE: 1997 Lexus LS 400 Fuel Filter location

The fuel filter is located under the vehicle on the left side before the rear axle.

SOURCE: 1992 Lexus LS400 wheel bearing replacement

I'M NOT 2 SURE BUT I THINK YOU HAVE 2 REPLACE THE WHOLE HUB WITH A NEW BEARING PRESSED IN IF NOT THE WHOLE SPINDLE

SOURCE: 1993 Lexus LS400 acceleration stalls or surges

I HAD THE SAME PROBLEM WITH MY CAR. 93 LS 400. THAT WOULD BE YOUR FUEL FILTER OR THE FUEL PUMP GOING BAD. TRY CHANGING THE FILTER FIRST. THE DEALER TRIED TO CHARGE ME $980 TO CHANGE FUEL PUMP.

SOURCE: manuals

I am new to the fixya web. I saw that you were looking for a manual. I hope that this information can help you find one if you still are looking.
　
　
www.lexls.com has tutorials
http://www.lexls.com/tutorials/
ebay.com has various manuals to buy
http://motors.shop.ebay.com/Manuals-Literature__lexus-ls400-manual_W0QQ_sacatZ6029QQ_dctZ1
or
www.books4cars.com
Here is a site that post comments and info.
http://www.lexusownersclub.co.uk/forum/index.php?showtopic=17916
or try
http://www.onlinefreeebooks.net/automotive-machinery-power-equipment-ebooks/
Also try your local library they might have a database you can use. My local library has database with Chilton car manuals.