This is from my post on Oct. 20, 2006 regarding a similar issue:
Update: My mechanic pulled a diagnostic trouble code of P0446 which relates to a service bulletin regarding a "false M.I.L. 'ON' DTC P0446 on some 1999 year ES 300's". The bulletin covers a certain VIN range which mine happened to fall under. This calls for the addition of Vacuum Control Valve (PN 25852-20010) which requires .5 hours. My dealer ended up charging me for 1.0 hours. They said the job was a bit more complicate than originally quoted. After waiting an hour already I gave them the go ahead (incompetent mechanic I suppose). Anyway, the part cost $34.09. I'll keep the forum posted if problems persist.
There is another recent thread regarding this problem...do a search, it might help.