1996 LS 400

also had timing belt(with water pump) replaced also.. all parts are BRAND NEW!!!!!!!!!

White smoke is generally an indication of burning coolant through the engine. It could be a bad head gasket or intake gasket problem.

mechanic checked engine, it is perfect....the white smoke is burning of fuel

Oh really? That's interesting.

Exactly.... Now you see why I am stumped

Yes, I certainly do

White smoke usually with a sweet smell should be coolant. Black or dark smoke with a raw fuel smell would be unburned fuel and gray should be oil. Has the cooling system been pressure tested with the plugs out to check for leakage into the cylinders?

this is whats wrong! im 99.9 percent positive! there is a switch on youre power steering unit, the vacuum hoses come off this switch and connect to your intake manifold. the switch is bad and the power steering fluid is being pumped up your vacuum hoses! to confirm this unhook your vacuum hoses to your intake manifold, put tape on your intake manifold tubes to stop the rough idle, secure youre hoses to something and see what happens! its not your motor! believe me! have you had to add alot of PS fluid lately?

oh yea, it might take a few days for the fluid to be burned out from inside your cylinders, but it will, i had my fault meesage reader connected to mine (because i had the same issue), and i would get missfire messages.