My lexus ls 400 model 1991 when start gray smoke ocurr for few second then disappear

Grey (blue) smoke at start-up is normally an indication of a leaking valve guide seal. A little oil leaks onto the valve and into the cylinder and burns away in a short whole. The leak is not big enough to cause constant smoke. The normal procedure would be to replace the valve guide seals and to check the valve guides for wear at the same time.

The smoke is from engine oil, it is caused by leaking valve seals , after the engine is shut down for the day oil is leaking past the valve seals and getting into the cylinders then when you start up the engine the oil is burned off, this is a common problem, and there is a couple of things you can do to help the problem with out taking the engine apart and replacing the seals, try this first at your next oil change add some Restore to the engine oil it will soften the seals and give them a little more life, if this does not cure the problem after a few 100 miles then you will need to have the seals replaced, and this is a costly repair, but you could just live with the smoke it wont hurt any thing just keep an eye on the oil