My 1992 LS400 with only 127000 on the clock has started to act strange on startup i get blue smoke for about 10 sec not heavy but noticable, also when cold it is running unevenly misfiring but as soon as its warm its normally ok anyone come across this before.

That is normally a sign that the air control valve on the power steering pump is not working and is allowing power steering fluid into engine hence the smoke and uneven running at start up.

Saying that it is normally a white smoke and not blue how clean is your power steering fluid are you using transmission fluid (red in colour).

Check your fluid level to see if it is low.

There are some posts on USA site telling you how to check valve.

Hope this helps let us know how you got on.

Either that or head gasket is on the way out....

more likely to be valve stem oil seals than head gasket if it is only on start up.

Blue = oil